There was an update today from Google for the CCWGTV, (200918.015), that seems to have fixed this, mostly
There is a new option under “Settings->Display & Sound”: “Surround Sound” that I switched on.
Under device “Settings->Display & Sound->Advanced Sound Setting->Surround sound format selection”, I chose “Manual” and turned on “Dolby Digital”
On Plex app settings, I’ve got “Passthrough” as “Optical” and “Optical Encodings” as “AC3”.
Now, when I play most videos with 5.1 surround, it’s getting properly transcoded to AC3, and my receiver is handling it. I do seem some issues with playback hanging for some (but not all ) videos with AAC 5.1. Not sure what the issue is there, though.
