The MPC 4K could basically control anything, just think about the chain in command and who is in charge...
You are using the controller MIDI out to trigger sounds within Reason, correct?
Now to incorporate the 4K into the picture, one of it's MIDI out ports needs to connect with the Controller MIDI in, considering it's the primary destination for those MIDI note/controller messages...
Can you see the picture?
I have a rack full of Modules, plus a couple of keyboards/controllers, and when I'll have the MPC 4K, everything will be logged onto paper because it could get pretty darn complex with the patching/routing...
The Savior of Darkness