Not sure how Plex handles DTS audio in MKA files.
I can tell you the Plex Android TV app does not handle multi-channel FLAC audio files well. Last I tested (see this post), it played the left and right channels and dropped the rest. This post is the last update from Plex I’ve seen on the subject (he was an employee at the time). AFAIK nothing has changed.
There is also a current thread about two songs playing at the same time on Android TV devices.
