mDNSresponder and avahi-daemon are not running, both are disabled in fc5 startup.
The machine has two ethernet cards serving as a firewall between the local lan (eth0) and the adsl modem (eth1). The firewall runs under firestarter, which I had to manually amend originally to get multicast operating correctly, which under default configuration does not route.
I should probably point out that whilst the soundbridge does not seem to work with the later versions (1528, 1539), running iTunes from windows is fine.