Yes, you could always mix them down, but no, there's no promise that they will sound right. The problem is cancellation, which is most largely a problem with heavily processed modern music, or (artificially generated) electronic music, less so with classical and jazz.
I agree with the Smyth Realizer, even though I've never heard it -- it's going to try to maintain the essence of the surround mix in a stereo mix. There are other ways of doing it, of course. There was a column on the subject in ...Absolute Sound, I think?...several years ago. He did it the other way, too -- used an artificial surround enhancement to make surround out of stereo mixes.
The other thing you need to worry about is whether or not you are buying a DualDisc -- those were thicker than either CD's or DVD's, so didn't play in all players.