I read in another post there's a thing called "Combatant" Tuvala.  Apparently, you can enhance a Tuvala beyond it's normal PEN level.  What is this?  How do I do this?

You can sacrifice part of your Narchillan equipment (1 armor and 1 armor, but not the whole set) to upgrade your Tuvala into "combattant" Tuvala through 2 quests.

Beware, once done you can't go back, think about it carefully! 

Yeah don't do that, it's not worth because you lose a Narchillia set.