Well, we do know for sure that the Leia/Tarkin-dialogue now uses different audio elements. All lines in that scene are now clear as day, whereas a lot of Cushing's lines had that "crappy ADR"-quality to them before.
They don't sound like different takes, though, and I doubt they were able to somehow mess with the original tapes - those lines have sounded tinny on every release up till now. I wonder if they were somehow able to clean up the original on-set dialogue?