5.1 Output through digital audio cable

Hi

 

I just resintalled my apple tv, and updated to the latest version of apple tv 2 and firecore.

On my current connection, I have my apple tv connected to a Sony Bravia TV through the HDMI cable and the Audio Digital Out to my Home Theater. The problem is that i cant get my receiver to undertand the 5.1 signal. I can play the sound, but it just recognizes the 2.0 sound. I use the same home theater for my xbox and it works just fine. Can anyone help me?