If you go into the Disc Setup menu when you play back a movie DVD, there should be an option for "Stereo" or "Surround" (or Dolby Surround).

All DVDs contain a stereo mix as well as a 5.1 mix but you have to select the Stereo mode. It might be labeled "2.0" (no subwoofer) or 2.1 (Stereo with subwoofer).

In that mode the center and surround information is all down-mixed (blended) into two channels with the left and right main channels.

Alan Lofft,
Axiom Resident Expert (Retired)