don’t worry about the forum layout 😉
Well, I’ve never seen “multicast to unicast” before. Anyway, a unicast is “normal” TCP/IP traffic if you will. That means its only directed at one (uni) recipient.
iTunes/firefly/whatnot don’t know about anything else in the network, so they adress the whole network. That’s called a multicast. So you should better disable this option and hope that multicasts are routed unaltered. 🙂