I'm trying to get my receiver to receive the Dolby Digital signal coming from the DVD player, but it only registers as Pro Logic. I'm using a Sony STR-DE875 receiver, and I think I have it hooked up correctly, because when I put in a DVD with a DTS track, the DTS logo lights up on the receiver display, and all the necessary lights come on showing that the receiver is receiving the DTS signal from the player. But I can never get the Dolby Digital light to come on on the receiver. It's just Pro Logic. What am I doing wrong?