All right, I wanted to update this thread because I did an in-depth debugging session with the 3090 and I *think* I've found a third compromise, which means no compromise on audio or video, but one on gaming... Here is what I did:
- I tried a clean install of Win10 x64 on a spare SSD (dual boot), with just MC installed. Got dropouts. This ruled out the software stack.
- I tried to take the VRROOM out of the chain, so I only had HTPC > X8500HA > TV. Got dropouts. This ruled out the hardware chain (besides the 3090 itself).
- I got a long audio+video freeze and realised that JRiver had just downloaded a new build while I was playing a film. I disabled auto-update and I've never had a long freeze/drop again (that was 10-15 films ago). If this is confirmed, I would call this a bug, because I don't see any reason for MC to do anything that could compromise playback. Could a dev confirm that MC only checks for a new build at launch, and not during playback? If it's possible during playback, could this be fixed?
Now, turning auto-updates off seems to have resolved the audio+video long freeze.
This means a few things:
1. The long audio+video freeze isn't specific to Atmos or bitstreaming, I experienced it (before disabling JRiver auto-update) on a DTS title using LPCM.
2. The 4xxx was most likely a fix for the micro audio drops, as what I remember was that I got long audio+video freezes, not micro audio drops. The possible network issue was likely a red herring. So if you have Atmos micro audio drops with a 3xxx GPU at 4K120, consider the 4xxx as a likely fix.
The 8-bit workaround mentioned at the beginning of the thread should have led me to test another workaround, which I used to use a while ago and forgot about, which is to have the HTPC on a HDMI 2.0 input of the AVR. This forces TDMS, and allows to have 4K23 in 10/12bits without any Atmos drops. You’re only limited to 8bits at 4K60.
This used to be an issue with some drivers newer than 532.03, as you would get a black screen when a HDMI 2.1 GPU was used that way, but it was fixed in 551.23.
Note that the output doesn't matter (both of the outputs of the X8500HA are HDMI 2.1 and I can use either without any issue).
I've now watched six full films with this set up (3090 >> HDMI 2.0 input >> TV) and have experienced no Atmos drops.
I'm going to do more checks to see if I can enable 8K Enhanced instead of 4K Enhanced in the AVR, and still get no audio drops.
I'm also going to see if I can bring the HTCP back to the HDMI 2.1 input and simply use a HDMI 2.0 EDID when I use it for video tasks (hence limiting it to a TDMS bandwidth) and then a full HDMI 2.1 EDID when I want to game at 4K120. But this will take a while and I wanted to share my third workaround right now, so others can test and see if it works for them too.
I might in fact keep the HTPC in a HDMI 2.0 input, as I can still game at 4K60 and the big advantage of doing this is I can use my Sony HDMI Headphones with the HTPC without having to put another VRROOM between the PC and the VAR to get the audio only to the Sony headphones.
One last thing, for those using a VRROOM, I kept having black screens with the latest fw, so I reverted to 0.34 (which happens to be the last fw with working JVC Macros) and the black screens seem to be gone.
So to summarise, here is my current workaround:
3090 HTPC with latest nVidia drivers (currently 650.81 studio) >> HDMI 2.0 input of the X8500HA >> VRROOM with fw 0.34 >> TV (Samsung S90C).
This gives me no audio compromise (Atmos + DTS:X), no micro Atmos audio drops, 4K23 at 10/12bits, no long video+audio freeze (auto-updates disabled in JRiver MC).
Main dowside is that I lose 4K120 for gaming, but I can live with that, at least until I get a 4xxx or 5xxx next year.
As always with HTPCs, YMMV
Good luck!