A much anticipated feature has made it into the latest version of iTunes (6.0.2). You can now stream to multiple Airport Express Base Stations, and play music on your computer speakers simultaneously. Well, kind of… I can’t seem to get it to work! I can play music on my computer, and on my Airport Express, but if I try to play them at the same time, the connection gets dropped to my Airport Express, and an error is generated.
You’ll need the Airport Express 6.3 firmware update in order to get the new “Multiple Speakers…” menu item. Good Luck!
Found via TUAW