XB1 does not support DTS audio output for videos unfortunately. This has been a FR on the XB1 forums since early 2014 with nearly 2000 votes and no update to this day.
I'm not sure how DeathSquirrel is seeing direct streaming. Is this just in the log? Anything I play with DTS audio shows that it is being transcoded.
Dunno, that's just what it shows in the admin console for that session when I play something. I tested it with the 7illusions app, which has the same playback engine, and I get the same claim in the server UI but that client clearly says it's transcoding the audio to AC3.