We spoke to Amazon, DTS-HD / DTS:X only passes through the DTS Core, so whilst its supported on the new device it cant pass all the channels through for the full effect.
We are still looking into the stutter that happens with DTS-HD playback, this appears to be a bug in the OS rather than in Plex. We’ve been able to reproduce the stutter without any framerate, refresh rate or resolution switching and have informed Amazon about the problem. We’ve yet to hear back unfortunately.
