I have a Harmon Kardon AVR-520 receiver that supports both DTS and Dolby Digital. I purchased the Microsoft Xbox High Definition AV Pack, hooked it up to the receiver with an optical cable, and enabled both DTS and Dolby Digital on the Xbox. When I pop in a DVD, the receiver indicates that it is receiving a digital audio source and I hear sounds from all 6 speakers. However, when I put in Halo (or any other game), I get no sound at all. The receiver indicates that it isn't receiving a digital audio source. Please help!