That's what I would guess. If they put a lot of money into the recording of the concert, they would've had a huge multi-track setup with a few of those crazy-nice (and crazy-expensive) Studer 24-track tape machines going, or perhaps even a fledgling digital system. I do know that 3M had just come out with a digital recording system at the time, so it's a definite possibility. Steely Dan was going to use this new system to record the Gaucho album, but their attempts to link two 16-track units together didn't work right and they reverted to analog tape. But as for the topic at hand, provided they had high-quality analog masters, it's very possible to remix the material from the source and get a high quality sound, especially with material coming from the late 70s when, in my opinion, recordings truly became hi-fi.