I use a PocketWizard Mini-TT1 on my camera and put my Nikon SB-700 flash on a PocketWizard Flex TT-5. Those units support TTL metering. They're kind of expensive but work flawlessly. I can adjust flash compensation on the camera and that will in turn vary the power output of the flash. I like the having the Mini-TT1 on the camera because of its low profile. It never gets in the way. You could get a Mini-TT1 and two Flex-TT5's for your set up.