Kodi should be clever enough to play 5.1 as 5.1, 7.1 as a downmix. It probably does exactly the same as your AVR would.
So 5.1 does make things much better, however instead of now having the horrible sound sometimes from the rears there is now a very slight clicking sound in the RR/RL speaker. This is happening about the same amount as before, so I’m guessing setting it to 5.1 stops the really nasty sound but is somehow still having this odd clicking sound sometimes.
Again this is only with Decode and passthrough does not do it.
You reported clicking sounds on the rear speakers, so could you please follow these instructions and provide some feedback:
- Login via the command line
- Edit the file
/etc/apt/sources.list - Add the following line:
deb http://apt.osmc.tv stretch-devel main - Run the following commands to update:
sudo apt-get update && sudo apt-get dist-upgrade && reboot - Your system should have have received the update.
Please see if the issue is resolved.
I also recommend you edit /etc/apt/sources.list again and remove the line that you added after updating. This will return you to the normal update channel.
This is not intended to solve the other issue, but PCM noise issues. If it does also solve the issue initially discussed here, please let us know. 
So far, seems good. Decoding TrueHD/DTS-HD and playing FLAC/PCM and setting back to 7.1 I can’t reproduce the squealing noise in the rear speakers and with 5.1 the clicking sound seems to be gone as well.
I’ll update if that changes.
Sweet! Can you also see/hear a difference in behaviour when playing the problematic titles you mentioned in the first post with passthrough?
Yea they still drop audio at the same points with passthrough enabled.
It may just be an issue with those files however : https://club.myce.com/t/atmos-audio-drop-outs-details-thread/399840/17
The odd thing, as people have pointed out if I play the actual UHD Blu-ray the audio is fine, and I’ve done direct rips of these as have many other people and for some reason the dropouts happen. Not sure what trickery my UHD Blu-ray player is doing to stop that.
And it’s just those two rips that are problematic?
Yep just those two, not found any other that have the same issue. It seems that they have a very high bitrate at certain points that causes the bitstream to break. It’s a known issue on lots of devices not just the Vero 4K. It’s just a little strange that some Blu-ray players seem to be able to not cause the issue.
Good that the PCM issue is gone for you now! We’ll get back to the Atmos sound drop issue some other time…