I'm not sure what your opinion of iTunes is, but, Apple's Airtunes works really well. Plug in speakers/receiver/whatever (either analog or SPDIF) into each Ai

I'm not sure what your opinion of iTunes is, but, Apple's Airtunes works really well. Plug in speakers/receiver/whatever (either analog or SPDIF) into each Airport Express. In iTunes, check each Airport you want to play through, and away you go. The audio sync is good. The Remote app for iPhone/touch works nicely with this kind of setup. Another option, which I think is more expensive and difficult, is Sonos.