I too had problems with my B2 to Sonos connectivity with a stereo setup in my Living Room. This initially worked fine with the early classic original Brennan app setup but the latest version wouldn't allow me to play music from the B2 to the Sonos speakers. The app indicated that the Sonos Living Room stereo pair were paused and although the track was playing no sound ensued.
I eventually resolved this by firstly un-pairing the two Sonos speakers.
Initially I still could not play to the Sonos speakers as the Brennan app still reported that they were paused. I think that one issue here is that the Sonos speakers (S1L's) are permanently on standby when not playing, they do not have a power on/off switch. Therefore if they have been used from the Sonos app and then paused the Brennan cannot "push" music to them. The simple solution (for me anyway) was to un-pause the Sonos app content, allowing it to play and then select the the Sonos speaker from the B2 app and "hey presto" success, the Brennan was able to "push" music to my paired Sonos set up..
I'm hoping this will hold up over time and I'll report back if there are any changes.
Wil