I have searched and trying to get the audio support för ATV/iTunes/iOS straight. I have gathered this much, so I would be grateful if some expert could confirm or correct my conclusion... ATV2: Plays AAC 2 ch no matter what. Plays AAC 5.1 but outputs this as 2ch through HDMI, but throughputs 5.1 through optical (but in general, most hifi receivers cannot process AAC 5.1?). Throughputs AC3 5.1 _only_ if optical cable is present (and ATV settings allow?), but cannot play files with only AC3 5.1 if no optical cable is plugged in. iOS: Plays AAC 2ch and 5.1 but outputs only 2 ch. Cannot play files with only AC3 5.1 The reason I am trying to get this straight, is how to convert my iTunes video library with maximum device-support and minimum hassle/converting. I have read that most hifi receivers don't know how to process AAC 5.1, but if that is NOT the case I guess it would be the best solution to have only an AAC 5.1 audio track since ATV2 can play it whether or not optical connection is present or not, and iOS devices seems to handle AAC 5.1 as well. But if it what I had read is correct, that most receivers can't handle AAC 5.1, then I guess I have to include AC3 5.1 _and_ AAC 2ch for maximum usability?