I always thought that the 70 mm cut of ESB had some audio mix differences, but no additional scenes, but this could be wrong. The 70mm mix of ESB is a bit more shrouded in mystery. As I suggested before, try watching Building Empire and see if that rings any bells. I think its on myspleen.

Someone asked if there was a bootleg of the ESB 70mm mix. I think its strange that there were bootlegs of Star Wars with the mono mix, but nothing for ESB. Something I would love to have someday is a copy of ESB with the 70mm audio mix as an alternative audio track, such as some have done/are working on for Star Wars.

I would love for something like this to be true and to come out. But the problem is that until it does, one is going to be sceptical.