Hi Mike,
I guess the difference between our situations is that I grouped the speakers with the Bluesound controller. That probably made Roon detect the group as a single audio output. I made the group in BlueOS because I wanted two speakers to act as a stereo pair (see this thread).
I will try to ungroup the speakers in BlueOS, then group the speakers in Roon while trying out the mixer control to get a stereo effect (as you kindly explained in the other thread). If that works I hope to have independent volume controls. I will test this later today and report back. And I wonder what happens if I group the speakers in BlueOS again after they have been grouped in Roon… The purpose of that would be to be able to use the Bluesound controller when Roon Core is unavailable.
Regards,
Frans