The six-track mix: it would actually be a 4.1 mix on a modern home theatre, not 5.1. The six channels were right front, left front, center, rear surround, and two low frequency channels. Since today's systems don't have this set-up, the two low frequencies would need to be combined into one channel. As far as I know, the six channel mix is the same as the standard 35 mm mix as far as audio differences go. But I could be wrong about that one. Now ESB had several differences in audio in the 6 channel mix, but that is another story...
The original theatrical stereo mix is available on the pre-Definitive edition laserdiscs and VHS releases, I think. The sound mix was redone for the defenitive edition laserdisc release. Since Editdroid is taken from the definitive edition, it would have the newer mix. I'm not sure there really is much differences between the two, but for the pure original theatrical stereo mix, one could take the audio from Rikter's DVDs, that were taken from the widescreen laserdiscs.