SilverWook said:

Apparently there were 70mm prints.

http://www.in70mm.com/library/blow_up/year/1979.htm

And those collectors film frames similar to the Star Wars 70mm frames had to come from somewhere!

Aha see according to that the 70mm only came out in 1982 as a double feature with wrath of khan, so even if there was a 6 track which there was in 1982 it could not be called the theatrical audio because it was not released in 79 despite the intent to do so. It was probably a very limited re-release not a nationwide re-release like star wars had and empire and jedi several times.

I would give a lot to see a triple billing of the 70mm of the oot of star wars, especially to see empire in 70mm.