DVD players output DD5.1 (or DTS) for movies. You need to go into the DVD player's audio menu and change the output from Dolby Digital to PCM or STEREO. This will down-mix the 5.1 tracks of discreet audio into 2 tracks (L&R stereo). Currently you are missing all of the audio that is intended for the center channel speaker and the surround speakers. Changing the setup is going to make you a very happy person!
Enjoy,
TIC
Enjoy,
TIC