I had an XX-1, upgraded from a 20X-H. The XX-1 is the precursor to the XX-2 (obviously) and was the first cartridge to introduce the flux dampening that pretty much al DV's incorporate now. there's a little switch on the front of the cartridge to engage or disengage it. That switch adds a lot of mass - the cartridge weighs 12g.
The XX-1 added a lot more finesse and "palpability" and texture to music over the 20X, but it lost the wonderful dynamics that the 20X does so well. The 20X sounded a bit like it had a loudness setting over the XX-1, which was smoother and more even all around, although less exciting overall. The XX-2 fixes these issues from what I understand.
Good luck