At some point in the last few iTunes updates, Apple finally included a feature that allows iTunes to stream to multiple Airport Express devices, as well as the host computer itself. Sweet! I’ve been waiting for this for a long time.
I tried it out in my hotel room (playing from my computer and Airport Express simultaneously) and it didn’t seem to work. But, it turned out that iTunes had perfectly synced the output devices. Once I muted the speakers hooked up to the Airport Express, I was able to hear the music coming out from my laptop, and vice versa. Wow, unexpected bonus.
Time to fill the house with Airport Express devices!