Deciding which AV receiver to buy is about choosing one set of features over another. Among units I've tested in the $400 range, this Onkyo is the one to choose for the sole reason that it has the best features.
Hang on, shouldn't it be about sound quality first? Sure, but all three midrange Dolby Atmos receivers I've tested recently --, and this Onkyo TX-NR585 -- sound very similar, and very good. Among the three I'd give the Denon and Onkyo a hair above the Sony for sound quality, but the difference is far from dramatic. The tie-breaker has to be "features for the buck."
"The buck" is kinda tough to pin down. The Sony and the Onkyo currently cost $400 while the Denon is $350, but that can change at any time, and all three have varied in price quite a bit recently. Let's call it a wash for now.
Another important consideration: Are you an Apple or an Android? The Onkyo and Sony offer the most flexible streaming options, including most importantly Chromecast built-in, which the Denon lacks. By contrast the Denon offers updated support for the AirPlay 2 standard. If you lean heavily to one or the other, let that be your guide.
In the end there's only a smidgeon of difference between the Onkyo and those two competitors, and all three are excellent choices. My ratings reflect that, with the Onkyo at 8.6, the Denon at 8.5 and the Sony at 8.4 overall. In the end, the Denon and Onkyo offer noticeably better sound, while Sony and Onkyo are more user-friendly -- but if they were all the same price, the Onkyo would be the receiver I would choose.
Tall, dark and boxy
I've written about the "safe" nature of most receiver designs before, and the Onkyo does look like many of its relatives. These are all black boxes, and they have knobs on. Compared to the Denon and the Sony though the Onkyo is a little taller at 14.93 inches. Keeping the same design does mean that the TX-NR585 retains my favorite feature of any receiver -- direct source buttons! Like most people I misplace the remote a lot and so being able to tap a button to get to the source I want is super useful. The Denon does offer four shortcuts, which is almost as good, but the Sony misses out on these completely.
Further enhancing user-friendliness, the receiver has a full-color, high-definition interface (unlike the Denon AVR740H) and a simple, powerful remote control. The Sony is nicer to look at and navigate, however, and so if you're using the menu system a lot this is something in the STR-DN1080's favor.
The TX-NR585 is a 7x 80-watt-per-channel receiver with an exhaustive list of features, including support for the atmosphericand formats. It offers a dedicated powered Zone 2 out if you're looking to set up another room with speakers.
The Onkyo receiver includes a bevy of streaming protocols, including. The receiver uses the proprietary FlareConnect system, which is essentially "mirror casting" for audio. It lets you "mirror" what's playing on one FlareConnect system to another, whether singly or throughout a whole house. The most useful application of this would be streaming a turntable or other analog source, though the onboard Play-Fi system also has this feature and a lot more besides.
In my opinion, the most consumer-friendly of all of these streaming systems is, not least because it's so affordable (from $35 for the plus $49 for the voice assistant). Meanwhile, the days of "one app fits all" are going away, with leader Sonos moving to support from within customers' favorite apps like Spotify instead. Though its rival Play-Fi is offered on more manufacturers' products, it requires the use of a specific app.