Hi Bob,
my experience is that B2 can be seen in the list of devices for Spotify Connect but is not usable.
The screenshot is from the Spotify Windows app running on my PC
My IPad similarly cannot play to the B2 but says that I need a Spotify premium account to use it but I don't have one.
My amp/receiver, Yamaha RN303 , is DLNA enabled, so I stream from PC to that.
I suspect its something related to the UPNP/DLNA services running on the B2.
John