To switch to music playback on the Home Theatre - In the Sonos App, just select the Home Theatre room from the slide up ‘room selector’ screen to bring that room into focus and then select any music source available/installed in your App, or ‘pinned’ to your Home Screen/added to ‘Favorites’ etc. and choose to play that audio on your Home Theatre.
There are many other ways to play music/‘other’ audio sources to Sonos speakers aswell, besides the Sonos App, including the following:
Hope that assists too - Happy New Year.👍