There isn't much difference in I, II and V when it comes to SL vs DL. DL maintains the original, unrecompressed picture quality from the source disc, but that's about it. VI has two other audio tracks and the unrecompressed video as well, but they're merely stereo and commentary options from the source disc. IV is the only one that has genuine audio benefits in the form of all those different audio mixes. The 1997 mix that Neil S. Bulk dug up is a gem. I just felt that IV needed some extra-special treatment.