So after an exhaustive search of forums and tech support, looks like it is the Plex app itself running on Sony Bravia Android TV's that is broken and only passing 2.0 via SPDIF (Optical). Sony has verified they are good on their end (all other apps properly send 5.1). Android confirms it handles 5.1 passthrough. Even Plex app inside another (Kodi) passes through. But the Plex app itself for Android fails to pass through the full audio.
Will Plex work to resolve this?
Thank you, love Plex, just need my 5.1!