If you’re running Logic Pro 9 on OS X Mountain Lion, and you have an Airport Express set up as a client on your (wireless) network, you can now choose ‘Airplay’ as an Output Device in Logic Pro’s Audio Preferences. This allows you to stream the audio that’s coming from Logic Pro straight to the Airport Express, to which you connected a home stereo or powered analog speakers.
It seems that I can’t stream the audio to my Apple TV – at least not yet (I’m on a mid-2010 Macbook Pro). That’s a bit of a shame, since for many of us TV is an important medium.
Changing the Sound Output in Mountain Lion’s System Preferences doesn’t help: when Logic Pro’s Output Device is set to ‘Built-in Output’, it will play over that output, regardless of the output you’ve selected in System Preferences.
Hopefully this will be addressed in a future update.