There's sometimes questions about the various differences in content between the various theatrical audio mixes on the original films, so I thought it was a good idea to start a separate thread for the few differences that appear in the magnetic 70mm six-track Dolby Stereo mixes compared to the optical 35mm Dolby Stereo mixes that's been documented so far.

STAR WARS

After they get out of the garbage pit and Chewie runs away frightened, the trash monster makes a sort of high-pitched roaring before Han fires a shot back into the doorway.

When the TIE fighters first appear in the Death Star battle; the first X-wing to be destroyed has a different/enhanced explosion sound. (There is also a short bit of the same screeching sound effect present which is listed below)

A screeching sound is heard where it in the 35mm Stereo was a short moment of silence just before the first Y-Wing (Gold Two) explodes.

When Han Solo takes out Vader's wingman in the trench at the end of the film the sound of the explosion is greatly enhanced.

THE EMPIRE STRIKES BACK

When Luke runs out of the wampa cave, there is a clear sound of his lightsaber deactivating. (This sound effect is actually buried very deep in the 35mm mix if you listen hard enough)

Different laserfire can be heard during the snow battle, the sound regurlarly used for TIE fighters instead of X-wings as heard in the 35mm mix.

The TIE fighter sound effects are different in the Imperial fleet establishing shot after Luke's failure at the cave. (Can be heard on the 2006 Bonus DVD Spanish and French audio tracks)

The establishing shot of the rebel fleet at the end of the film doesn't contain tracked music. The two additional shots of the fleet added to the 35mm version required the tracking of a section of "Yoda and the Force" to precede the cue "The Rebel Fleet".

Lando's line "Luke, we're ready for takeoff." is a different take. (The same take later reappeared in the '97 Special Edition audio mix)

The exterior shot over which Lando says "When we find Jabba the Hutt and that bounty hunter, we'll contact you." is not in the 70mm version, instead when Luke says (voice over), "Good luck, Lando" the scene cuts directly to inside the rebel cruiser where Luke says, "I'll meet you at the rendezvous point on Tatooine."

Lando's line "Princess, we'll find Han. I promise." is a different take.

RETURN OF THE JEDI

The opening crawl on the 70mm prints used the music John Williams scored for the opening crawl to The Empire Strikes Back. *

* Source: Film Score Monthly, SE album editing and assembly supervisor, Michael Matessino.

Credit goes to David Morgan and Belbucus for providing in-theatre audio recordings of the 70mm presentations so that it was possible in the first place to document these differences and to hairy_hen for pointing out some of the more subtle differences. Please help add to this list if there's any differences not yet mentioned here.