"AUTO" is on a rotational scroll when pushing the yellow PURE button on the remote. It scrolls through Direct, Pure Direct, and Auto. It's not the best way to do this for sure, but it is what it is. "AUTO" will keep selecting the "Default" sound mode shown in the chart on page 262 of the AVR-X2800H owners manual.
To get the receiver off of "AUTO" mode, you need to select either Pure Direct or Direct. You are NOT Leaving this sound mode on. After selecting Direct or Pure Direct to get the receiver out of AUTO, select sound mode DTS-HD for a DTS-HD 5.1 soundtrack. This will be remembered every time you watch a DTS-HD 5.1soundtrack. Select Neural:X instead if you are listening to a DTS HD 2.0 for 5.1 speaker surround sound. This will be remembered every time for a DTS-HD 2.0 soundtrack.
As far as the display. it Is very clear with it's abbreviations to show what sound mode is active. It can't fit the entire word so abbreviations are needed. It also shows the HDMI input at the same time which is just as important.
I talked to Denon out of curiosity on this subject and the way I took it from them is that these upmixer sound modes are always shown even if not needed, as customers like to see them in the sound mode list to avoid confusion. This is NOT a bug. They are only active when they need to steer sound to additional speakers. With the case of Dolby, they are used for the Virtualizer. When they are selected with a 5.1 speakers system, they are doing very little but looking for the virtualizer option or additional speakers. They are essentially idle with a 5.1 speaker system without using the virtualizer or additional speakers. I would use DTS-HD or DD+, instead of the added Dolby Surround or Neural:X as I'm sure it's just adding another layer of digital noise and the such, while still leaving the base, fundamental sound signal output essentially the same.
I returned my Onkyo receivers for what I consider quirks. Mainly I couldn't get past that the TX-NR6050 and TX-NR6100 with a "7.1 speaker setup" using DD/DD+ with NO upmixer, switching the side surround outputs to the back surround speakers with a 5.1 signal input and output. Onkyo even states NOW in the new and correct updated manuals that with a 7.1 speaker setup, playing a 5.1 signal input, that the side surround channels will play out of the "Back" surround speakers, and the side surround speakers will be silent. IMO, improper steering logic and outright incorrect. Some have speculated it was due to Onkyo being cheap and not wanting to buy the proper licensing for correct channel steering. I don't understand why they would do this. It's very detrimental when listening to 5.1 Concert soundtracks where I want discrete sound without upmixers.
The other thing was their display, shown in the picture directly above this post. When I was not using an upmixer, the on-screen display would show 5.1 > 7.1 when it was still a 5.1 signal being output. It seems since the logic was incorrectly steering the side surround channels to the back surround speakers, it considered this 7.1. INCORRECT. So it displayed 7.1 whenever the back surround speakers where turned on. It was like 1 wrong, equaled 2 wrongs. Just poor design IMO.
Then Onkyo never had their owners manual correct for either receiver. Only after I argued with their support did they ever put up the correct on line manuals. The original manuals stated these receivers were only compatible with 24Gbps video, not 40Gbps. This stated the receivers were only compatible with 8K30p "UNCOMPRESSED" video or 8K60p "COMPRESSED". The correct manuals were finally put up that stated the receivers were compatible with 40Gbps video stating they were compatible with 8K60p "UNCOMPRESSED" video.
The TX-NR6100 sounded very good with Stereo signals however the TX-NR6050 did not as it has some compressed dynamics in the bass.
I returned the TX-NR6050 mainly for the sound quality but also the quirks. I returned the TX-NR6100 as I didn't feel comfortable owning it. It was designed with quirks, customer support was mainly clueless, and I didn't trust the receiver or support to continuing working correctly in the future. I really was concerned about Firmware upgrades. A firmware upgrade can break a device, or include additional features as Denon has added in the past. I didn't trust Onkyo support, their firmware upgrades, or their hardware reliability, so I returned it for another Denon that I have confidence in.
This is only my opinion and take, as I know others love their Onkyos over Denon and Yamaha.
So what ever floats your boat. As I said on the other forum, I believe you would be happier with another Onkyo despite their shortcomings IMO.