Glad to hear you got it sussed out. I've been using ipads/iphones as controllers like this for a while, mostly using the Lemur app by Lline (now discontinued), and TouchOsc (still available). The Flux:fx app designed with Adrian Belew was a lot of fun effects designed to be manipulated with an XY interface, but I had issues getting it to properly run with the Axe (whether via an external audio interface or plugging the ipad directly into the Axe's sub port).
Now that midi over Bluetooth is becoming common, I've fired those controllers up again (previously I had to hardwire the ipad to my rig). There are certain control functions that make the best sense with foot manipulation, and others that benefit from finer hand movements. What I like about the Lemur/TouchOSC approach is variety of control types (radio buttons, circular knobs, XY pads, sliders, and even gyroscopic control) and logic functions that provide triggerable scripts.