This is new. I didn’t notice this before.

I have an airport express. It’s a power brick with a 1/4″ out. So I can play music over wifi. When you have wifi enabled, the Mac sees the airport express and puts this dropdown in iTunes automagically.

First, you click at the bottom.

Now you can select multiple outputs and it’s all in sync (I walked back and forth between rooms)!

Vista needs to have this sound card aggregation crap. It’s super-cereal.