I don't know very much about sound production, but I think that while sometimes alternate takes and edits are used for the soundtrack, the scene you seek should be the same take on the cds. The problem is that all the soundtracks have different mastering and EQ than the movie.

Your best bet is 7FN's transfer of the Star Wars LP. I'm guessing this should sound closest to the movie. If that doesn't work, then you could try the 1993 Anthology cd or hairy_hen's adjusted isolated score version of the Special Edition Soundtrack (the stock SE soundtrack has really harsh EQ). Good luck!

Edit: I remember that You_Too made a filtered version of the center channel of Star Wars specifically for voices. He used a different program then audacity so it might be a better starting place for you. If doesn't still have this I still might.