Wouldn’t multicast only be utilized if one had multiple linked zones? Where you want all endpoints to be fed one identical stream from the Roon source in perfect sync? I link 3 to 4 zones myself.
I’m asking, not saying this is the case. Just surmising so. I can’t see a reason for multicast of one doesn’t link zones but every reason for it if one does. But I’m no authority on either the network protocol or relation to roon.