Sadly it looks like it won't work on the Aftershock / Kingmaker. The external expression X Y input is tied to the 4 physical pedal knobs rather than independently assignable so don't really gain any additional control. But the External tap function does let you switch channels etc.
However it looks like the C4 does let you assign the expression X Y independently so may still be some interesting diy control possibilities.
I'm all ears....