Page 1 of audio probs with xbox

I have a JVC TH-A35 home cinema and I recently bought a XBox. I connect my XBox to my JVC amp using the optical.When I enable Dolby Digital in the dashboard of the xbox I get no sound at all from my games but my amp shows that it is receiving digital by showing 6 spkrs on the lcd display.However,when I disable dolby digital,I get surround sound no problem.(2 spkrs on the amp lcd) This proves that the optical is ok. But could it be a problem with the streaming from the xbox. Maybe an extra bit in the coding is preventing the JVC amp from decoding it?

I piped another dvd player into my JVC using the optic and my JVC displayed the 6 Spkrs (showing that it is seeing the digital signal) and gave me an audio o/p. Xbox and JVC helpdesk`s havn`t been much help. :(