There will be no difference from the stereo version and the '93 mix, because I did not alter that part of the track in any way. It is completely impossible for any part of the SE mix to have ended up in the main channels, because the main channels of the SE were not used at all. Phase-cancelling isn't really going to work completely either, for several reasons: one, the upmix likely altered the phase relationships of some parts of the sound; two, different lossy encodes cannot be completely recombined in this manner because different parts of the total sound have been discarded or retained; three, the 5.1 track is a few milliseconds delayed compared to the stereo version; and most importantly four: the stereo tracks on the disc probably have DialNorm applied, which reduces the total volume of the audio, while the 5.1 version does not, and therefore comes across at exactly the same level as the source laserdisc track. It is simply louder by a consistent amount, which I know very well can cause a lot of confusion about what sounds better or worse.
There does seem to be something a little bit different, but nothing about it sounds wrong to me, and I believe that the above reasons (which are out of my control) should explain any discrepancy. The only other thing would be if something went drastically wrong with the AC3 encode and upper harmonics of the bass somehow ended up in the main channels or something, but I highly doubt this is the case. I don't know if that's even possible, actually. If it did, I should think the result would be a lot more distorted.
Satanika, I'd be grateful for any help you could provide with the flyby. At this point I'm pretty sceptical that what I've been trying to do can actually work, but I've been wrong before. I ended up deleting my prior attempts, but I'll send over the source files and we'll discuss it.
Made some more progress last night, so now I only have the beginning section of the movie to work on before moving to the LFE channel, though I may do a bit more tweaking to the quad laser battle. I've again been able to retain more dynamic range from the '93 mix by keeping the replacement sections shorter, and I've also been more conscientious about the exact synch and phase than before. The improvements tend to be subtle, but I'm pleased with them. Still haven't decided what I'm going to do about those two surround effects, though, because I can think of convincing reasons both for keeping and discarding them. Anyone else want to weigh in on those? To restate, it's the echo when the Jawas blast R2 in the canyon and the 'slipstream' or whatever when the Millennium Falcon is in hyperspace just before arriving at Alderaan, and I can't decide whether to think they were '93 additions or part of the original mix.