"V-STACK is a 32 Bit VST-rack that expands a VST System Link network by adding 16 VST instrument slots and is ideal to play VST instruments live on stage"
Brainspawn Forte - hands down.
It's a bit annoying to figure out how it works properly, but once you do it, the program does absolutely EVERYTHING a keyboard module does PLUS a lot of other nice stuff. For example: after you configure it right, you can use a pedal (sustain pedal) in the controll input of your controller and play an entire pre-defined gig without even looking at the computer screen and just changing the presets sequencially using the pedal. http://www.brainspawn.com/