With only one center brace on a 6 foot tank I would also use only 2 bulbs,.. you can use the center and edge areas for
lower light corals, and put the really high light stuff in the center.
I think 2*400W 14K 10" off the water in a 140 would be a good light setup

It will be a power hog, but it will do fine.
THe real question is what kind of corals are you planning to keep?
Whiskey
__________________
Mr. Jive/Dr. Heckyll
And you run and you run to catch up with the sun, but its sinking
racing around to come up behind you again