Bug with streaming audio to Apple TV# Sat Feb 2, 2013 by brett
So it appears that there is a occasionally a problem in streaming music to the Apple TV from the Mac. The symptom is that you can see the “Audio TV” device in your Sound -> Output window, but every time you try to select it, the selection reverts to the “Internal Speakers” line.
The easiest way to reset this, is to go up to the menu bar at the top of the screen and switch off your Wifi Network, leave it off for a second, then switch it back on. When you reconnect to your wifi network you should be able to select the “Apple TV” device in your Sound/Output pane in the System Preferences.