How do you have it connected to your system? Are you using analog interconnects from the Oppo to you receiver/pre-amp? Are you using a digital connection (optical, coax or HDMI) from your Oppo to receiver/processor?
Based on your description of the sound, I'm guessing you are getting correct sound from CD, but for DVD I think you are only getting the discreet L&R front channels of sound and you are missing the discrete sound that is intended for the center channel/surrounds.
This could just be a setup problem. Go into the Oppo and set the sound to "stereo or PCM", especially if you are only using 2 speakers in your setup. If you are currently set up for dolby digital output, but only have 2 channels of amp/speakers, you may just be missing the sound intended for the center channel and surrounds.
Enjoy,
TIC
Based on your description of the sound, I'm guessing you are getting correct sound from CD, but for DVD I think you are only getting the discreet L&R front channels of sound and you are missing the discrete sound that is intended for the center channel/surrounds.
This could just be a setup problem. Go into the Oppo and set the sound to "stereo or PCM", especially if you are only using 2 speakers in your setup. If you are currently set up for dolby digital output, but only have 2 channels of amp/speakers, you may just be missing the sound intended for the center channel and surrounds.
Enjoy,
TIC