The more I think about this, the more I think the easiest solution for me is to have the Aux In routed post-Volume, pre-Master Volume, so that the Master can still be used to control overall levels including external gear, but guitar volume can be defeated in case you only want to hear external gear, particularly in cases where the external gear is being fed guitar signal from the KPA send.
Just writing to confirm and notify others that this is exactly the behavior implemented in firmware 2.0.1. THANK YOU Kemper; this is a HUGE improvement for me!!!