I gave this a try without success. I have some AppleTV encoded movies that will play in Surround if I use apps other than iTunes (e.g. using Plex). I went through the steps in this hint and although everything looked OK in terms of matching what the hinter wrote I get absolutely no sound output if I select the Surround audio track. Sound is fine with the Stereo track. I made sure iTunes volume was at 100%. Also note when I switched the Surround the receiver did not detect a surround input from the Mini (which it does if I use other apps like Plex).

I'm testing this on a late 2009 Mac Mini running Snow Leopard. Movies were converted using HandBrake 093 with the Universal preset.

I just realized I left out a pretty big step. You need to have perian installed and simply run this command in Terminal.

defaults write com.cod3r.a52codec attemptPassthrough 1