I’m not very hopeful. My guess is that the “surround sound” on the DVD has been synthesized from the original mono audio, so it is probably phase shifted from the centre channel and so normal “cancellation” methods won’t work. If this is the case, then I’d expect the results to sound tinny and horrible, which is what you go on to describe.
There’s a discussion about other tools / techniques that may be helpful in this topic: Reduce voice not eliminate but I’m not optimistic.