I dig this concept, but I believe you are better served with Dmitri's Megadrum. I am about to buy a 56 input module from him, and for 255£, I believe that you are better served with it, for what you aim to do.
The module is rack mountable like the Alesis DM5, but you can fit it on a rack, has positional sensing all around the pads, and 56 inputs man, you can have a monster kit.