The MotorMix's control protocol is similar to, but enough different from the MCU and HUI protocols, that those controllers will not serve as a MotorMix substitute. One critical difference is that the MCU's LCD has less characters, and the MIDI commands to control it are different.
As far as controlling the VCS from something like Push 2, or using the Push's displays, that would require custom software interfaced to Push and communicating directly with the Pacarana using either MIDI or OSC.
We have a product, vKA, that transforms the Akai APC40 into a VCS controller by emulating the MotorMix with the Akai (no LCD support though since the APC40 lacks a display). Our vM2 product does a similar thing except it provides a way for a Lemur template to do the same. Lastly our vKiP iPad app uses the MotorMix protocol to provide a full-featured VCS touch control surface.