Sonos does not support DTS HD audio, so it’s likely transcoding the audio to Dolby stereo on the fly. Try playing an A/V Dolby Atmos audio file via VLC instead - here’s an example you can maybe try…

https://media.developer.dolby.com/Atmos/MP4/Universe_Fury2.mp4

@kontinosxon 

Also if available as an option, you can set output to DTS 5.1. There’s always a 5.1 DTS core within the Signal that Sonos would be able to play. 

The link doesn’t work but I have already downloaded this Atmos test file the universe fury from Peter’s Pee and when I play it via VLC I still get Dolby Digital Plus 2.0 

Strange, the link works for me. Anyway if you have tried it, then in that case it might be the App you’re using. I can’t see it being the Sonos hardware, in this instance, as you mention it works with your other Apps, Netflix etc. 

@kontinosxon 

Are you playing the file via vlc app? If so, on what device the app is running? 
Imo there could be two different reasons… settings of vlc or settings/ limitations of the device the app is running on. 

Yes via vlc app on the Sony x950g with default settings and have tried both enabling and disabling digital pass through mode found in vlc settings. 

@kontinosxon

If the same file plays multi channel on another device than the tv and vlc settings are ok, I suppose it’s a limitation or a bug of the vlc app version for the tv os. 
If other apps on your tv play multi channel, it’s not a general limitation to stereo for apps on the tv os.