Do I just need to go into the X3 and tell it which cc commands are assigned to each IA?
As a default, the delay IA on the X3 turns off the reverb on the KPA!
Yes, that's exactly it. The fact that the delay switch turns off the reverb tells us that the X3 sends MIDI CCs like you want.
Unfortunately I have never looked into the X3 in such detail so I can't help you but you can probably find this info in the manual for the X3.
Good luck!
Mats N