Recently I bought an Apple Airport Express, a marvellous little device enabling me to stream music from iTunes to my stereo. Everything worked well until I enabled my firewall, at this point iTunes could no longer connect to the speakers.
Searching around the internet I found that iTunes uses port 5353 to stream but opening the port in my firewall did nothing to make it work.
Using Active Ports I saw that a couple of connections to remote TCP ports 5000 and 6000 were trying to open to the Airport Express. Opening these remote ports in my firewall turned out to do the trick.
Thought I’d pass the info along as my searches through the Apple forums yielded nothing more than, “just turn off your firewall”