I think I just figured this out on accident. I have a q800t tv and have been having the same issue. Bought a ps5, hooked directly to the 2.1 port, sound going back to receiver on hdmi 3. Pcm always showed as stereo. I could sometimes get Dolby digital 5.1 to work but with significant delay and I think that's compressed. I have the dh790 receiver with update for earc. I decided to switch cables I was using. I hooked the cable that came with the ps5, a hdmi 2.1 cable, as the earc cable, and just using the "high speed" 2.0 cable to the TV. I can get full pcm sound from the ps5 now with no delay. Now I just need another 2.1 cable for the video so I can get 4k/120. I was using generic best buy high speed cables with ethernet previously. Which is suppose to be good enough but I'm guessing it's not. Tv settings set to passthrough with no delay.
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