CatBus said:

As for the audio changes, all three distinctly different theatrical soundtracks for Star Wars are well-preserved and you can listen to the alternate versions yourself.

I don't know if I would dare go as far as to say the 70mm six-track mix of Star Wars has been well-preserved (by Lucasfilm maybe). h_h's work is truly magnificent and I absolutely love it but you have to remember that it's still only a well made approximation of that mix, lots of guess work involved, especially in terms of the LFE-channel. I get what you mean but it's just that I see the words "preservation" and "restoration" tossed around so often around these parts...

CatBus said:

As for the other movies, ESB of course had two totally different cuts, and we've only seen/heard the 35mm one on home video or preservations, and just a list of changes for the 70mm one from people's memories.

There actually exist more than just a list of changes from people's memories. 8mm film sequences and even an 1980 in-theatre audio recording has surfaced. You should definitely check it out if you haven't, great stuff: http://www.wideanglecloseup.com/starwarsaudio.html