Vero 4k+, LG CX, Apple TV 4k and Sonos Arc

Of course , but doesn’t contradict what I wrote. It seems you just look at “what does it say on the display” without really answering the question. (And I do welcome being corrected if I’m wrong, it’s not that) Does it properly mixdown 7.1 to 5.1 or are the extra back surround channels just discarded?

I am not sure what to make of the post you linked or even that you understood me right. What I mean is: is the following information from this post from 2018 still valid or has it been fixed (I guess @Chillbo could chime in): 5.1PCM being converted to 7.1PCM - how to stop this? - #4 by Chillbo

As I said, it just discards the surround back channels, even though it “supports it”. The following thread is only 2 months old, so I’m pretty sure it’s still valid: https://en.community.sonos.com/home-theater-228993/sonos-arc-and-7-1-downmix-to-5-1-6863804

You are right, that is why I posted the optimal settings. Although I remain somewhat skeptic of your magic ears, let’s agree that for all practical intents and purposes, the ARC isn’t gonna reveal noticeable differences in sound quality regardless of LPCM og transcoded AC3.