I am making an external control panel, with a bunch of buttons and an MPG.  I use a galil controller and plan to connect the MPG direct to the controller using an aux encoder input.  That should be straight forward but I need to add switches to select which axis and what feed steps.  Searching the forums here the usual advice is to write a "Brain" to do that but I have found no guidance on how to do that.

I have another idea how to do this and I would like some feedback on its feasibility.  For the various buttons I am using an iPac2 keyboard emulator to send Hotkeys to mach3.  So my idea is to use the iPac to send the appropriate messages to select the jog rate and selected axis.

Yes, that works fine.  I mapped Alt - A, B, C to set the active axis for the MPG.  So the MPG went through the Galil card and the axis selection and rate go through the iPAC2 emulator as keyboard shortcuts.