Really interesting how your log shows MPV checking a lot of formats.
I joined another thread about Optical output failing, and ran my own tests of a film with 5.1 AC3.
I didn’t get any sound, and I found that the player was trying to load an ac3 encoder into the chain instead of Direct Playing what it agreed to Direct Play, just like you found.
As far as your MPV decision goes, if you have direct stream setup, your server is allowed to send you the flac files unchanged. On the player if you have Direct Play set up, then the player has to decide whether it can output those flacs directly to your device. The decision looks to be in the hands of MPV, at first glance.
So you might try the standalone MPV or the one in the HTPC client if it’s accessible, ran in verbose mode . That’s what I did to isolate a playback issue I had.
I can’t send FLAC to my DAC. So I can’t help as much as I’d like.
