The X-Y tracking in reacTIVision makes it perfect for controlling complex mixes. Using multiple channels playing the same sequence with different voices allows you set up vector mixing similar to the vector synthesis found in the Prophet VS.

I got this to work pretty well - I still need to figure out how to have constant levels though. The levels drop to 50% during x-y mixing There's only one crossfader in Live, which I used to mix between the 2 planes, so I'll have to find some tricky way to get the mix level constant. (I later solved this problem) But other than that, it works great - I've got 2 sets of 4 tracks, each track with it's own VST and 1-note sequence, you can move around the 4 tracks in x-y, and mix between the two sets. Here's a video of the setup in action - it really give a good visual sense of how the mix is happening.



I'm controlling both planes with the same controllers and mappings, so the x-y position is the same in both planes. You could just as easilty reverse the tracking in one plane or use a second set of CCs to give you arbitrary control in both planes. This could also be played live, with all tracks responding to a keyboard.

Here's the CC mapping:




This screen shot shows the routing - click  for the full-sized image: