Will -- my experience on Maui is that Koa is protected and very expensive when you can find it. No live trees can be cut, so the wood must come from trees that have fallen.
I made a parlor guitar a couple years ago with the back and sides being Black acacia, and it is quite loud for its size and complex in its sound.
Koa is in the acacia family of trees and my guitar looks a lot like koa only a bit more honey colored. For a more complete discussion of the sound qualities I would try one of the luthier sites, or maybe LMI or StewMac guitar supplies.
Blessings
Barbara