Optical Sound

I just installed the latest version of atv flash but I am having problems with sound. (running 4.4)

I have the atv connected via optical cable to my receiver and have enabled ac3 and DTS in the menu, plus set audio to 16-bit. When I play a movie the sound plays but the receiver doesn’t detect 5.1, it just gets stereo sound.

It works fine with XBMC so I’m not sure what the issue is with atv flash.

Any help would be greatly appreciated.

Thanks