What music sources can be sent to more than one A1-MR simultaneously?

Any audio source can be used for multiroom playback through your A1-MR(s) when using AirPlay, or when streaming audio via DLNA / UPnP, or using the streaming services integrated into the Audioengine Control App. The A1-MR(s) need only first be configured into groups using the Audioengine Control App.