Vquestor,

Prog. Change or Bank select will only do just that - prog. change or bank select. I don't think any manufacturer will overlap these codes with arranger controls.
For Ketron X1/X4/SD1, you can get the programmable 13 or 6 switch controller and use your foot to select the arranger controls.

What are you using to generate chords to feed the arranger? Can it send sysex?

Henry