In case you are still in search for a better quality of the Leia hologram dialogue, have you tried to use the one from “The Story of Star Wars” LP. The sound on the LP is mixed directly to 2 channel, no matrix-surround encoding, and you can try using the 2 channel music mix of the variety of LP releases. I would start with the music LP presentation that came out on CD from the Polydor label and work your way up.
EDIT: A correction:
The music over the Leia hologram at the Lars garage was available commercially in 1977, however, the music over the Leia hologram at Obi-Wan’s home would begin to be available in 1997 by RCA Victor and later Sony.