Surround sound issue

[Solok]

Ok this is probably a simple fix and I am just missing it. But can't seem to figure it out.

First my setup:
Samsung LN52a650
Yamaha RX-V663
Panasonic DMP-BD35K

All are setup via HDMI cables.

Problem:
Whenever I play a blu-ray on my player, I am able to hear the full 5.1 surround sound. However, if I play a DVD on the player, it only plays through the fronts and center. I always go to the audio setup of the DVD, to ensure it is able to play 5.1, and it still will not go through the rear speakers. I have it setup to run bitstream and DRC is off. Anything else you can suggest would be appreciative. Again, it is probably something simple that I am missing.