On the off chance that this is a sincere post, and not just someone jerking us around, here's what looks like the only real answer. Obviously you don't want to get rid of that beautiful and expensive Garmin. I think that you'll have to go with a MUCH smaller tank bag, maybe just enough to hold a wallet, set of keys, and a small handgun. Then the GPS could be mounted much lower in the view, and allow you to see the gauges. The C14 has pretty good space in the saddlebags, and if you don't have one already, you could add a topcase to get more storage.
I've toyed with the idea of mounting my Garmin above my gauges, behind the middle of the windscreen. It's not like I'm ever looking through it at that level anyway. That would also allow me to glance at the Garmin without taking my eyes off the road ahead, which is a plus. With a GPS as big as yours, you might be able to use it INSTEAD of a windscreen. (okay so I couldn't stay completely serious, sorry).