The receiver boasts a 384kHz/32-bit "Hi-Grade" DAC in addition to DLNA and USB playback with support for most music formats including DSD.
This Onkyo is one of the first to announce support for both "object-based" surround formats, but there's still very little software available for either protocol. At the time of this review, a total of just 13 Dolby Atmos encoded Blu-rays are available,That's a molasses-slow ramp-up, and there's no reason to believe the rate of Atmos released Blu-rays will dramatically rise in the next year or two.
The other object-based immersive audio format, DTS:X is just launching this month, with the release of a sole Blu-ray, "." DTS is mum about how many DTS:X discs would be launched this year.
Due to the complex demands of Dolby Atmos speaker setup, we decided to use the TX-NR646's AccuEQ Room Acoustic Calibration program to set volume levels for our Pioneer Elite Atmos speakers and subwoofer.
We were happy to note the procedure requires the user to run the entire calibration routine from just one microphone position, which greatly eases setup compared to systems that use multiple locations. The resulting speaker balances were fine, except the subwoofer volume was much too loud, so we manually turned the sub's volume down.
We started our TX-NR646 auditions with "The Better Angels," a little gem of a film that covers a small patch of time exploring Abraham Lincoln's youth in rural Kentucky and Indiana. The soundtrack's ambient canopy of birds, buzzing insects and wind rustling the trees' leaves was startlingly realistic. With these sounds of nature, the TX-NR646's resolution of quiet detail was exquisite. Switching over to a Sony STR-DN1060 receiver, the sound was perfectly fine but diminished the sense of place we heard from the TX-NR646.
Next, we watched "American Sniper" to see how the TX-NR646's played this film's Dolby Atmos soundtrack. Did Atmos' height channels add anything to the sound that we didn't hear from standard 5.1 surround sound? Yes it did, but the effect is subtle, and the film's spare use of Atmos height channels makes it all too easy to forget that they are actually doing anything.
The intense combat scenes played nice and loud, demonstrating the TX-NR646's abundant power reserves with better dynamic punch than the Sony. The sheer clarity of the Onkyo's mayhem and dialogue were excellent. We tried out the TX-NR646's Phase Matching Bass feature that promises to "suppress phase shift in the midrange to enhance bass sound," but heard no difference whether the feature was turned turned on or off.
Next. we played a few Dolby Atmos promotion demonstration videos designed to show off Atmos, first on the TX-NR646 and then on the STR-DN1060, which lacks Atmos capability. The differences between the two receivers were much more obvious. The STR-DN1050's spatial dimensionality was smaller, more speaker-bound than what we heard from the TX-NR646. Demos are one thing, but the real-world difference between Atmos and standard Dolby TrueHD movies will be subtle. We didn't have any DTS-X encoded films on hand to try a comparison with Dolby Atmos films.
We were initially concerned that the TX-NR646's Atmos processing was limited to just the front-left and -right channels. Would the front speakers' envelopment seamlessly match with the side surround speakers? It turned out that front-to-rear sound balances were very good. And since we had our surround speakers set up a foot higher than our heads' seated height, the sound always came from above. This higher placement strategy for surround speakers has been recommended by Dolby for as long as we can remember. Now, with front-channel-only Atmos systems like this Onkyo, mounting the surround speakers high makes even more sense.
With that in mind, perhaps front-only Atmos left and right speakers will be more than adequate in some rooms, like the relatively compact CNET listening room. This approach also reduces the cost of assembling an Atmos home-theater system, since your current surround speakers may not have to be replaced.
We did one more round of TX-NR646 and STR-DN1050 comparisons, this time with music from the Rolling Stones' 2008 concert "Shine A Light" on Blu-ray. It has a non-Atmos soundtrack, but even so the TX-NR646 came out ahead. Its energy, dynamics and power made the music more exciting, while the STR-DN1060 sounded a bit softer and more bland in comparison.
Connecting Bluetooth to oursounded good, with unexpected detail in midrange-oriented tracks. It didn't get screechy or break up with guitars as some implementations can. Swapping to Spotify Connect, however, showed us what we had been missing, with more treble bite and even greater detail.
The Onkyo TX-NR646 is an awfully impressive receiver for the money, and it sounds terrific. It's just as proficient as the Sony STR-DN1060 but sports better dynamics, and its features are skewed toward home cinema. Dolby Atmos and DTS:X are nice extras but not the real reason to buy this model. It gets our recommendation because it makes movies sound good regardless of which proprietary format they're in.