Voodoo Lab

So im picking up my Axe-Fx in about a week and obviously i need a midi controller for it. I decided on the Voodoo Lab Ground control pro because it seems to be by far the best option, only thing im not sure of is what expression pedal to get for it. Im looking for something that will feel similar to...

so ive got a marshall jmp-1 and im thinking of buying a gcx and ground control pro to switch pedals and change channels on my amp. ive got it all worked out except i cant figure out how i would connect the jmp-1 to the gcx. to my understanding by reading all the manuals, i should connect the midi th...