I am ALWAYS getting the VDI caught in the HD volume pedal, no matter what I do. I would LOVE to have a VDI wireless setup.
I suspect they are using at least two of the pairs - one for the signal going from guitar to the pedal, like a typical guitar signal, but likely digital, but maybe its a straight analog. The other is some kind of talk back to the guitar, sending instructions for tuning and model. The POD to Variax is probably not a constant signal, but an instruction on patch change that the Variax listens for. Then again, maybe its sending a heart beat type signal.
Anyway, the system is relatively closed, so we may never know. Like you, I'm a software developer, and so find it fun to speculate.