DVD: Strange issue with speech.

I have an issue with DVD playback in both MP and MC. This doesn't happen with every DVD I play, but with many/most of them. The volume on the vocal portion is very low to the point of being inaudible. The background noises and music are all perfectly loud. Basically I can hear what's going on in the world but when people talk it's like they're mouthing the words. I'm guessing it's because DVD audio is on multiple channels and there's something wrong with the way my system is handling one of them?

Audio from mp3 or non-dvd video works perfectly fine.

I'm using a SB Audigy SE.
I have tried installing from the Cd and also uninstalling and using Daniel K's support pack.
I'm running a newly installed copy of Windows 7 Ultimate x64. I had this same problem on my previous install of the RTM version of Win7. While using the RTM version I installed the Shark007 pack to see if any filters would help. Nada.

When I use the onboard sound instead I do not have this issue. I suppose I could switch to using it but I'd like to use my card if I can.

This computer is my media center so I really need DVD playback to work.

Any ideas? 'Cause I'm pretty frustrated.