Er... problem fixed.
I was able to come buy a set of calipers from a low mileage '05 Busa. Since they are the same calipers as the TLR's doing the swap was fairly simple.
Over the course of this past year I had been coming to the conclusion that the Brembo ratio (19x18 verse 19x20 driving 6-piston calipers) wasn't the issue but that the calipers themselves had issues. The thing is it is easier and about the same cost to get newish used calipers than it is to get a seal and piston kit. Sure enough, after the system was bleed with the new calipers on I had power in the lever I had never felt before!
One task down... a few more to go.