However… I’ve had a sticky problem for the last year – 50% of the time iTunes or Airfoil just can’t see all of the Airport Express boxes. I’ve spent a lot of time researching Bonjour (aka Rendezvous, zero touch, multicast DNS) and doing packet traces. No joy. Everything looks fine; the multicast DNS is working fine over 5353; the radius is within limits; firewalls are non-blocking; the data is not crossing a router. I was stumped.
Tonight I think I fixed the issue. As part of de-cluttering for the impeding house move I took my last 802.11b device off the wireless subnet and bumped the configuration to be exclusively 802.11g. Instantly everything started working.
So in summary: Airport Express, Airtunes, iTunes and Airfoil really work well on an exclusive 802.11g network.
Hope this helps someone else.