See this thread: Apple TV 4K - Can PMS send the Dolby TruHD or DTS HD stream directly?
And info from Infuse: Audio Options (tvOS) – Firecore Support
dts/dts-HD is converted to PCM on the AppleTV whether using the Plex app or Infuse. PCM is lossless, so there should be no loss in audio quality.
Plex and Infuse handle TrueHD differently, but it still ends up getting passed as PCM. Any Atmos information is dropped during the conversion.
