Hi,
Could be possibile to add an analog audio source as ADC Hifiberry or an USB audio card?
My objective is connect a raspberry to my amplifier (with cd source) and stream the music to another room.
cd -> amplifier -> Musicbox ->>>(multiroom)>>> other Musicbox -> speakers
Possible yes, but you’d need a mechanism to switch between your analog input and the rest of musicbox. I don’t have any any plans to integrate something like that, it’s quite niche.
Damn! I just installed MusicBox hoping to move straight on to this. Oh well +1 
Seems a bit convoluted, but you could do
cd -> amplifier -> web stream -> Musicbox ->>>(multiroom)>>> other Musicbox -> speakers