Instead of throwing more powerheads in the tank, what about opening up the rockwork more or reduce the footprint of the rockwork.
Imo, you have enough pumps........it's the aquascape that's restricting flow & creating detritus piles.
Sometimes eliminating rock comes at the expense of getting rid of some corals, but it sure makes maintenance easier. I don't care for the look of crowded rock wall of coral so it works for me.