There was in interview with Matt Wood who said that all of the mixes were captured and archived.
http://www.hometheaterforum.com/community/threads/lucasfilm-on-star-wars-the-complete-saga-blu-ray-part-ii-matthew-wood.307875/
QUOTE:
Q: Was there any thought given to archiving previous tracks like the 6-track master from the 70mm prints or the 78 mono remix? Any thought given to putting them on the Blu-ray?
A: Yes, we have those and they’ve all been digitized. I don’t know if they considered putting those on the Blu-ray. That might be more of a question for Marketing, it may be an issue of space. It’s funny because I play those other audio tracks, like the scene when R2 and C3PO have been left on Tatooine and they walk through the canyon. I just love that on the current mix, you can actually hear the quiet, when R2 is lonely, going through the canyon. I played the original mix and it’s FULL of hiss and totally brittle, so it’s fun now to hear it like George wanted it to really be, what was intended.