My setup is as follows:
CCwGTV → LG GX → Sonos Arc. Neither the TV or the soundbar supports DTS decoding OR passthrough. Plex is set to HDMI passthrough. I tested a few UHD Blu-Ray remuxes, and the results are as follows:
AC3, EAC3: passthrough (with Atmos)
Any DTS track: Plex client decodes to multichannel LPCM
TrueHD: Plex server transcodes to EAC3
So it looks like at least Plex it knows the AV system doesn’t support DTS whatsoever and decodes to LPCM, which is actually preferable because DTS-HD MA tracks remain lossless this way. On the other hand for TrueHD the server has to transcode to a lossy format, which is both inefficient and losses quality. TrueHD Atmos is lost in the process as well.
When I set Plex to not do passthrough, DTS still decodes to LPCM but all Dolby tracks transcode to AAC on the server and decodes to LPCM on the client. So it looks like Plex does not have a Dolby decoder on the CCwGTV at all? What I would like is for CCwGTV to tell Plex to decode TrueHD to LPCM like it does DTS.
