I have an Apple TV in the living room and an Airport Express in the bedroom. I can play music in the living room through Apple TV, or play it in the bedroom through the Airport Express (which is also connected to a stereo). I can control what song I want to hear, and which room to hear it in, with the remote app on the iPod Touch.
I have my Apple TV connected in two ways: first there is a HDMI out to the TV.
Then I also have an OPTICAL audio out going DIRECTLY to the receiver. This allows me to play music through my receiver without having to turn the TV on. However ,you need the remote app to see your music library instead of seeing it on your TV screen.
Hopefully this helps?