This was an idea I had in where I incorporated a stand-alone DrumKat, mounted it on a custom rack, added 2 PoleKats, and 4 Vis-U Lite cymbals.  I plugged the PoleKats and Vis-U Lites into the trigger in's of the controller.  I  assigned the high-hat sounds to the PoleKats, cymbal sounds to the Vis-U Lites.  This gave me 18 playing surfaces.  The kit now looks and reacts like a real drum kit, but it is more compact and tight.  You can midi the controller into any sound module, or attach to a laptop with with sound software, or even a sampler.  I really love the design, and the entire footprint can be picked up and moved easily by 1 person.