As you know, people who updates own iTunes on Mac to 8.1 version has a troubles with Firefly DAAP server (not only with FreeNAS).
I found this post, where described the solution of this problem, http://discussions.apple.com/message.jspa?messageID=9195702#9195702
If exactly, user cstrouble wrote:
"I also had the same problem with a FreeNAS 0.69 based Firefly server. After analyzing the traffic with tcpdump, I concluded the problem was with Bonjour and not DAAP because no DAAP traffic was initiated.
The problem appears to be the lack of a TXT record. The built in Firefly mdns code sets one up, which is why using Firefly to advertise the service works. If using Avahi or mDNSResponderPosix (e.g., on FreeNAS), adding a TXT record with "txtvers=1 iTShVersion=131073 Version=196610" is sufficient to get things working. My working mdnsresponder.conf entry for FreeNAS/Firefly is:
txtvers=1 iTShVersion=131073 Version=196610
Similar changes should work for other NAS or homegrown systems using Firefly with Avahi or mDNSResponderPosix."
I check this method and it really work with my Freenas 0.69.1.4461 and my MacBook + iTunes 8.1.
I think, need to change some files (as /etc/rc.d/mdnsresponder or may be other ?) and put this string "txtvers=1 iTShVersion=131073 Version=196610" into configuration file mdnsresponder.conf