The advantage I can see is that, although you are adding another keyboard to the rig, it would be simpler, as far as trying to properly route the midi config and turning off the SK1 if you wanted a solo voice from the exterior module.
Thanks
Bernie this is where an "ALL IN ONE" Arranger like the KORG Pa4x would shine for all what your trying to do,...and you would be carrying way less gear to the gig..
...good luck with your music!