When B&O had the MasterLink (ML) solution this is how it all worked. You could press N.Music or CD and then “Speaker 1” in the remote menu. Beosound music would play through the TV speaker. “Speaker 2” would activate any front stereo speakers and so on.
Turn on a music source and video sources would be killed and visa versa.
The BR1 and current-day web based products have an inherent linking of sources but which makes speaker selection difficult other than the default TV controlled speaker choice. I am sure it can be done….its just the infinite combinations which the manual does not tell you and only the most expert of installers will know how.
The last time I recalled using the BeoApp on a “true” Beovision (Eclipse), there were mybuttons on one of the back screens on the app. With the BS Theatre, this is now done a differently way.