The 2100 had several other changes. For one you didn't have to pre-select the endings as you did on 2000. They also addressed an error in the vocal processor (in the high voice preset). By the way they denied that the error existed for the entire life of the 2000, even though they sent me an elaborate workaround for it.
It was important to me because at the time I was working a lot with Dean Mathis, of the New beats, and I used it to do the high part on their big hit Bread And Butter. The 2000 was the only KB on which that preset didn't work right.
I'm sure there were a few other "upgrades" but nothing they couldn't do today with simple software fixes.
As I recall this was about the time they developed the technology to do updates without having to physically replace a board.