Not sure I understand. Sonos devices don’t connect to each other using HDMI or optical, they connect using a LAN signal, most often WiFi, although in some cases they can work in a wired (Ethernet cable) fashion.
Where they use either HDMI ARC or optical is when connecting to a TV, in order to get the audio from that device into the Sonos ecosystem. Optical connections are bandwidth limited to Dolby Digital, HDMI ARC (specifically eARC) can handle MAT/Atmos, although a regular ARC signal can carry the Dolby Digital Plus version of Atmos. 

I also do not understand your question. The same music source can be played in multiple Rooms by using the Group feature.