I just tried installing Kodi on my Sheild - and then the Plex plugin in order to access my Plex server that has multichannel FLAC files. Everything is set to pass-through and yet my AVR sees stereo. See here: PM4K / PlexMod for Kodi (18, 19, 20, 21, 22+) - Plex Players / Streaming Devices - Plex Forum
Kodi versus Emby: only that users have reported that they can play multichannel FLAC files. See the intial post above here.
