Dunno if this helps shed some light on your situation, but here is what I wrote in another thread...
"So, I just ran a test of the Xbox One S bitstream settings against my PS3. Both are connected to my AVR. The AVR will indicate via lights on the front panel if the signal is Dolby Digital or Dolby Digital TrueHD or DTS or DTS-HD MA. I can also get that info displayed on the TV screen via a button press on the remote. This is particularly helpful because it shows the incoming signal - in some cases it's a 7.1 stream as well as the output - in my case a 5.1 stream since I haven't acquired the extra 2 speakers for my receiver which is fully capable of 7.1.
I played a DTS-HD MA disc in the Xbox and it registered as simple DTS on my receiver. Played the same disc in the PS3, and the receiver showed DTS-HD MA.
Set the Xbox's bitstream output to Dolby Digital and tried with a Dolby Digital True HD disc and the results were the same. With the Xbox, the receiver showed Dolby Digital 5.1, with the PS3 it showed Dolby Digital True HD.
So the Xbox is just playing the Dolby Digital and/or DTS core and not the full track. As someone mentioned above, the best solution is to set the Xbox to output uncompressed PCM 7.1 or 5.1 depending on your speaker setup."