As one of the leaders in audio/video receiver development, Denon is often the first to market with the industry’s latest innovations in home theater audio and video capabilities.
It’s not surprising to us then that Denon’s AVR-X6400H audio video receiver stands as one of the most advanced and complete AVRs in market this year. The receiver offers up to 11.2-channels of surround sound without the need of extra amplification and supports each of the three most popular 3D/object-based surround formats — including Dolby Atmos, DTS:X and Auro-3D–for up to 7.1.4 speaker setups.
The lesser-known Auro-3D surround format offers three-dimensional sound fields playing compatible soundtrack mixes.
For greater flexibility, the receiver provides eight HDMI 2.0a/HDCP 2.2 outputs (including one in the front) that support 4K Ultra HD with high dynamic range (HDR). The baseline HDR10, Hybrid Log-Gamma (HLG) and Dolby Vision (with dynamic metadata) profiles are all supported. It also provides three HDMI outputs (main/sub/Zone-2 for) added flexibility.
With three HDMI outs users can simultaneously output an image on two different devices such as a TV and projector, in addition to content from a different A/V source in a remote location.
More impressively, the AVR-X6400H will be one of the first AVRs that will be able to support the enhanced Audio Return Channel (eARC) feature that is to be a big part of the forthcoming HDMI 2.1 standard. Enhanced ARC will enable sending more robust and bandwidth-hungry surround sound formats like the lossless Dolby TrueHD and DTS-HD Master Audio formats along with Dolby Atmos and DTS:X 3D surround sound enhancement over the eARC connection on next-generation TVs (coming in 2019 and beyond).
The lack of sufficient bandwidth over the currently available HDMI-ARC has been a bottleneck in getting some of those high-resolution audio formats out of a television to the built-in decoders in AVRs and will be one of the most compelling reasons for adding HDMI 2.1 once testing and SoCs are broadly available to support a wide range of devices. (Note that no testing procedures for HDMI 2.1 were in place upon the release of the AVR-X6400H, so it is unlikely to support all of the characteristics of the HDMI 2.1 spec, but as home theater audio goes, eARC is a huge feature.)
Meanwhile, lovers of legacy analog formats will be pleased to find the AVR-X6400H includes a Moving Magnet (MM) phono cartridge input to hook up a new or legacy turntable to spin a collection of vinyl records.
Additionally, a pair of optical digital audio and a pair of coaxial digital audio inputs are included along with two sets of analog component video and four composite video inputs.
Other connectors include an Ethernet port for cabled broadband connectivity, a pair of DC12V trigger outputs, IR in/out ports, and an RS-232C serial connector for custom home integration needs.
Digiphiles will find the receiver also supports streaming a variety of Hi-Res Audio formats over Wi-Fi at up to 24bit/192kHz, including DSD files.
In addition to the front HDMI input, the front panel of the AVR-X6400H includes a USB port, full-size headphone input, a jack for the Audyssey room calibration system mic and a set of composite audio/video inputs.
Front inputs and physical control buttons are all concealed behind a down-opening black cover panel mounted directly underneath the receiver’s large blue fluorescent dot-matrix display screen.
Remote
Despite the ample selection of on-unit control buttons and large round source and volume control knobs, most of the operation will be done through the supplied remote control. The remote carries a large logically laid out button array that is well labeled to make it intuitively easy to figure out and use system features, with very few hidden functions.
The remote calls up a variety of clearly laid out graphical user interface menus that pretty much step users through system setup and adjustments.
For those who find it hard to put their mobile devices down, Denon makes available a HEOS app for iOS and Android smartphones and tablets. This works as an app-controlled heart of an AV home network.
Users can wirelessly connect to popular streaming services and networked storage devices via Bluetooth or Wi-Fi through the app, calling up favorite artists or songs, or tuning in a favorite streaming service or Internet radio channel.
Support For Next Generation Devices
In addition to the aforementioned summer firmware update bringing eARC capability, the receiver also can be adjusted through the setup menu to support newer devices running more advanced and newly emerging A/V formats and specs, like the Xbox One X, Roku 4K HDR streaming media players and others. This will ensure support for things like enhanced 4K/HDR using cables rated for up to 4K/6GB (prior to future firmware updates).
It also includes a few less obvious diagnostic tools, such as the ability to test HDMI cables and to determine their bandwidth and speed rating, to help trouble shoot or at least identify compatibility issues as new standards and specs begin to emerge. Denon has really gone the extra mile with this receiver.
Sophisticated Components
Internally, the AVR-X6400H receiver incorporates sophisticated custom power transformer, DACs and other components, in addition to four high-speed fourth generation SHARC DSP processors. Combined these processors deliver continuous processing capability of 10 GFLOPS (10 billion floating point numerical computations per second) for a host of sounds and effects).
The receiver generates 140 watts of power into 8 ohms with 2 channels driven, offering enough on-board amplification for all channels without the need of an additional outboard power source.
However, when additional power is required, the unit carries 11.2-channel pre-outs for use with an AV preamp and added external amplification. Full Bi-Amp mode is also provided to drive traditional 5.1- or 5.2-channel setups.
The receiver’s built-in multi-room capability enables listening to two different sources in two different rooms at the same time. This will let someone watch a movie in full surround sound in the main listening room, while wired stereo music is piped into a room in another part of the house.
Cosmetics
As AV receivers go, the Denon AVR-X6400H maintains the basic black box look, with styling changing very little over the past 10-plus years. The unit measures 17.1-inches wide. 6.6-inches high and 15.1-inches deep and has a gloss black metallic finish with a large hinged panel cover concealing auxiliary HDMI, USB and analog composite inputs, full-size headphone jack, mic jack for the built-in auto calibration system, and various operational control buttons to manually access menus and settings without a remote.
Room Calibration
The Denon AVR-X6400 includes a sophisticated auto calibration system, called the Audyssey Platinum Suite with Audyssey MultEQ XT32. This adjusts the speaker balance and tone to the best parameters for the configuration of the room, taking into account eight seating locations. At the end of the calibration, the system also recommends the best overall volume level for the amp under optimal home theater listening situations.
Audio purists can still manually tweak the system to fine-tune levels with golden ears or sound meters, but we think a lot of will find the auto-calibration system more than adequate to dial in the proper balance for an extensive multi-speaker set-up, particularly where object-based audio soundtracks are concerned.
Among other benefits, MultEQ XT32 provides Dynamic Volume adjustment that anticipates loud sounds to help keep volume levels even when desired. In addition, Dynamic EQ improves dialogue, bass response, and surround channel levels at lower volumes.
The system’s Sub EQ HT enables individual calibration of two subwoofers to provide even and balanced bass response around the listening room, as Low Frequency Containment reduces the amount of bass to prevent disturbing people in other parts of the house.
The auto EQ system comes with a mic to pick up room tones in order to auto adjust separation, tonal nuances and volumes from each speaker configuration in relation to the different seating locations around the room. The system accounts for the number and type of speakers measured and then adjusts for reverb and reflections off of walls and objects in the room. It will also adjust for up to four overhead height channels in rooms intended for object-based audio experiences.
After the XT32 system optimization procedure, we found music to have realistically flat, balanced low end for music and pleasingly dynamic sound for movie soundtracks, with optimal adjustment for up to eight seating positions.
The results were impressive playing both 2-channel and multi-channel content, but the latter seems to get an especially impressive benefit from the room adjustment. Listening to a 5.1 SACD mix of Elton John’s Honky Chateau, the sound was impressively natural and realistic, and the improvement was clearly discernible in an A/B comparison between “direct” and XT32 output.
The XT32 system also supports Audyssey’s Dynamic Volume, which is very convenient for watching/listening to action movies with dynamic soundtracks without disturbing anyone in another part of the house.
MultEQ XT32 auto setup and room calibration delivers balanced, dynamic sound with enhanced surround performance for as many as eight seating positions.
For more personalized tweaking, Denon sells an aftermarket Audyssey MultEQ Editor App permitting advanced users to deep dive into sound setting.
Multi-room Audio Distribution
As the 2017 flagship, Denon’s AVR-X6400 makes use of the company’s full HEOS whole-home wired or wireless music distribution system, which enables sending music to supporting HEOS wireless speakers and other HEOS-enabled products positioned in multiple rooms around the home.
The Denon AVR-X6400 was also one of the company’s first AVRs to support Amazon Alexa’s Smart Home Skill for Entertainment Devices. This adds the benefits, via connection to an Alexa-based smart speaker with far-field microphones, of accepting spoken commands to playback video and music programming, hands free.
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With vocal commands, users can activate the receiver to play a favorite streaming music service and send the music to another networked HEOS-enabled device or wireless speaker placed almost anywhere in the house. Supported Internet music services include TuneIn, Internet Radio, Pandora, Spotify, Amazon Prime Music, iHeartRadio, SiriusXM, Soundcloud, Tidal, Napster and Deezer. Vocal commands can also be used to enable switching between inputs (Blu-ray, DVD, Media Player), turning volume up or down, pausing, muting and playing the next song.
Streaming with Alexa voice commands is easily set up by opening the Alexa app, selecting “Skills” and adding HEOS Home Entertainment to enable. From there, Smart Home in the Alexa app menu can be used to choose Devices and Discover or say “Alexa, discover my devices,” which will enable engaging the X6400H or any other HEOS-enabled device on the network.
Even home servers, like a NAS devices or networked computer hard drives, can be accessed to play digital music collections stored in a wide variety of file formats in brilliant clarity. We sampled Led Zeppelin’s 2014 Remaster of Physical Graffiti ripped to lossless FLAC-44.1kHz/16 bit and were impressed with the full natural sound reproduction of Bron-Yr-Aur, which in Dolby Surround mode, seemed to continuously circle us with the warmth of acoustic finger picking spinning around the room. High notes chimed brilliantly without being harsh, shrill or fatiguing to our ears.
The sound of the streamed digital version was indistinguishable from the CD it was pulled from.
Mid-tones were similarly natural and full, as we heard in the golden harmonies of the Mamas and Papas singing Straight Shooter, and in the strained vocal growl of Jim Cappaldi’s lead on Traffic’s Light Up or Leave Me Alone from the Low Spark of High Heeled Boys CD.
Despite the more dated recording technology used on Wilson Pickett’s I’m A Midnight Mover, the AVR-X6400H delivered real life to the classic vocals and horn response.
The AVR-X6400H also offers a nice assortment of DSP listening modes that offer a variety of surround sound or enhanced two-channel effects. These include all of the standards, such as Dolby Surround, DTS Neural:X, Matrix, Rock Arena, etc. and even the less common, Auro-2D Surround, which produces a full punchy 2D sound for music. All of these are fun to experiment with, though I found regular stereo to be most satisfying for the bulk of my CD listening, preferring the mastering and mixes on true DVD-A, SACDs, and Pure Audio Blu-rays for my main multi-channel listening uses.
As good as the AVR-X6400H is at playing music, it may be even better at delivering the impact of deep loud explosions, or roaring truck engines from a 4K Ultra HD Blu-ray movie channeling Dolby Atmos 3D surround from a lossless Dolby TrueHD stream or DTS:X from a DTS-HD MasterAudio soundtrack.
Such soundtracks relayed by this receiver offer enough impactful punch to vibrate the room while faithfully reproducing soft whispers and subtle clicks a trigger. Both audiences and Hollywood directors should be well pleased.
What’s more the AVR-X6400H is a 3D-audio monster, offering support for four overhead channels, front, center, rear, side-firing speakers and a pair of subwoofers, and three 3D audio formats, including the less-well-known Aural 3D.
Unfortunately, we didn’t have any Aural 3D content to sample, but Dolby Atmos and DTS:X (upsampled from 5.1) soundtracks were impressively immersive, with clear and precise dialog, playing both sampled effects tracks and 4K Ultra HD Blu-ray releases, like Guardians of the Galaxy vol. 2 with Dolby Atmos object-based surround, and the bombing low tones of Atomic Blonde in DTS:X.
Conclusion
With all of its latest and greatest features, it’s truly hard to believe that the Denon AVR-X6400H is a step down from the new 2018 flagship AVR-X8500H that was introduced at CES 2018. That beauty will ring in at $3,799 and provides a bump up to a full 13-2 channel system, while including all of the features and capabilities of the X6400H and a little extra. We believe this receiver offers just about everything the most discerning audiophile could want without going the much more expensive route into separates. Further, Denon has seemingly done everything currently possible to make the X6400H ready for the future of home theater entertainment. It might never be fully HDMI 2.1 ready, but it will support that digital interface’s new eARC feature (coming with firmware update expected in July), and despite the onset of ATSC 3.0 TV broadcasts, 8K and other A/V technologies, it’s hard to believe that this will receiver will be rendered obsolete anytime soon.
Indeed, this receiver reproduces both old and new audio and video soundtracks in surprisingly detailed and subtle quality to provide the realism and musicality that should excite most listeners.
The Audyssey MultEQ XT32 room calibration system is among the best in its class for both accuracy and for improving the sound for clarity and musicality from the settings out of the box, or even what we were able to tune in by ear. We found dialog after the MultEQ XT32 adjustment to be perfectly balanced against the supporting sound track while listening within our review space.
At $2,199.99, the Denon AVR-X6400 will be out of the price range of some, but for discerning audio/videophiles, the features, benefits and performance will provide a real value at this place in the market.
We therefore award the Denon AVR-X6400H five out of five hearts. 
The Denon AVR-X6400H used for this review was a company loan.
By Greg Tarr
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