Ideally, wouldn't movies use AAC instead of AC3 to compress multichannel audio? And can't an Apple TV output 5.1 AAC properly to a receiver? If so, why do people go to so much trouble to get AC3 into a MP4 container? is it because most receivers can only decode AC3? If this is true, then are there any receivers that can decode AAC into 5.1, and if the Apple TV can't decode AAC into 6 channels, will it just output it in stereo?