I'm not thinking of this necessarily as a BASS effect - though it could be - but as a general MIDI-driven synth. There are a LOT of them around, some dating back to the early 1980s, and I just have little experience with this sort of thing; mostly I've only done softsynths. But if you had to recommend, say, three units - analog, digital or some combination of the two, synthesis or sampler, etc. - what would you go with? It'd be great if they were rack-mount, but that's not a hard requirement.