Just my 2 cents on the topic... It`s been 2 days that I have been struggling getting the ATV2 to work with XBMC with my Film library and I just nailed the last issue... AC3 5.1.
Hope this will help people around as this thread pops first in Google but the place I got the solution does not. Furthermore, the solution I found was not listed in this thread.
Set Up
Apple TV 2 with IOS 4.3.3
Jailbreaked with SeasonPass
XBMC 10.0-7
Using HDMI cable for sound.
Setup in 5.1
AC3 passthrough activated
Yamaha RXV-1600 as a receiver
Video used, M2TS with h.264 video and AC3 5.1 audio created using MeGUI and muxed using TSMuxer
With this setup, I was getting static noise like a lot of people and to solve the issue I followed this...
http://www.sinfuliphone.com/showthread.php?t=77544
Basically, I went in the Apple TV 2 Audio setting
Activated Dolby Digital (just in case as it was not)
Set to 16 Bit instead of Auto.
And it workes now.
Hope this will help some people, who like me never thought Apple TV general setting would impact XBMC.
Cheers