Bought The Flamming Lips Yoshimi DVD. Its has sound option giving stereo sound and also a full 5.1 option. When I set it to out put 5.1 the DVD player is doing so but my amp only reconises it as a digital stereo image. The amp is a panasonic XR45 and its connected to the DVD player via an optical cable. When I play movie disk the amp alway picks up the 5.1 signal no problem. Is there some setting I need to change?