Hi @Paul_ku.
Welcome to the Sonos community and thanks for reaching out to us. I understand the situation so let me help you out with that.
If the Sonos 5.1 set up home theater system is set to receive audio from the TV, the surrounds would be on surround mode. They will only be in stereo mode when playing music through the Sonos App as what you have described above. Currently, this situation is fixed as is Since the home theater system still depends on the codec from the TV and the codec of the video source. I would like to ask if we can try setting the TV audio quality to PCM and then try the twitch music stream and see how it goes. (this is just a shot in the dark) Since the source would still be the TV and that the codec is still depending if the TV is generating a 5.1 surround audio or regular stereo. However, allow me to send this to our engineering team so they can take a look into this matter as a feature request. I would advise subscribing to this thread and through our announcement topic for any feature updates, feature release, and bug fixes.
Please let us know how it goes. We are always here to help out.
Thanks,