I have the original Xanadu DVD, and it sounds pretty good!
Now that Tron has been reissued, the Ebay mania should die down enough for me to score the old non-anamorphic Tron with the 4.1 mix.
I have a couple movies with 3.0 mixes, (Zardoz and The Adventures of Mark Twain) that were only stereo on Laserdisc, so apparently the DVD's sport theatrical mixes?