I've got the ARC and a pair of ERA 100s set up as a surround sound system. 

I understand that this disables Bluetooth on the 100s but what I don't understand is why I can't initiate music from my Pixel (Android) device? (The Sonos or ERA 100s are not an option to play back on.)

If I go through the Sonos app to play back music from YouTube Music, it's a much more limited app. I can't just browse the YTM library.)

Is this how the Sonos is supposed to work?