One of the true 1977 mixes has been on home video – pre-1985 releases of Star Wars have the 1977 stereo mix. The best quality audio of the 1977 stereo mix was from a pan & scan Japanese Laserdisc, and is included with most preservations.

In terms of dialogue, there’s no difference between the 1977 stereo and 1993 mixes. In terms of sound effects, the obvious one is the shattering glass sounds during the cell block shootout. A lot of fans (myself included) think of these additions as precursors to the Special Editions – the 1985 mix was at least a mashup of the various theatrical mixes, but the 1993 mix brought in stuff that was never in the films before. I’m sure there are other changes too, but I just don’t listen to the 93 mix that much (for that reason).

As far as sound quality goes, the 93 mix is probably technically the best-sounding official Star Wars mix ever made. But I just can’t get past the non-theatrical elements, so I prefer the 77 mixes (hairy_hen’s six-channel reconstruction is my favorite).