Only going from memory here, so FWIW. The original 800RB had that trademark GK sound vs. the 1001RB/2001RB, which sound similar, but are less obviously colored tonally. It's never been my expectation that the 1001/2001 were supposed to exactly mimic the 800. GK now makes legacy amps that do just that. In many ways I prefer the 1001RB since it isn't as narrowly focused, tonally.
Comparing the two series is more like comparing siblings as opposed to identical twins. Many similar characteristics, yet just a tad different.