Hi Drog
Yes, that's pretty much what I was doing with my old amp and pedal board setup.
I ran one output from guitar to my RJM Mastermind PBC which went through all my pedals etc and into the guitar amp.
I ran the other output straight into a little Session Gordon Giltrap GC10 preamp and XLR out from there to the PA.
I could mute or activate either signal at the touch of a button. Electric only, pieazo only or combined. I could still do that with the Kemper although it would mean having extra power to front of stage and a separate stand-alone pre amp pedal. It's not the end of the world but it would be REALLY cool to be able to do everything within the Kemper for convenience and total control.
I know that the main input sockets are mono so clearly it wouldn't be possible to send both signals into the front input without Kemper redesigning the hardware. However, it should be possible to add this feature (if it doesn't already exist and I just haven't figured it out yet) in a firmware update like the parallel path feature.
If you could use the Front input for Electric signals and the Alternative Input or Return Input on the rear for the Piezo signal, the two signal paths could remain completely independent until the main output.
Electric would go through the Stack including the cabinet block but the alternative input would bypass all of this and probably enter the signal path just before the reverb. Alternatively, they could just add the ability to assign the rear inputs to the parallel signal path (for some effects) simultaneously with the front input going to the other side of the parallel path for the electric.
I should probably add this to the feature request posts rather than here.