Actually, 2x400 would cover a "normal" 6' tank without any major problems given the right reflectors and height above the tank. The problem is with the 33" tall, being that PAR would be very low in the middle deep ranges. I ran a 6x2x2 180 SPS heavy but mixed tank for years with 2x400's.
If you're keeping SPS, I agree with the 400+250+400. for the best spread/penetration of light. If you're keeping softies/LPS, 3x250 would likely work.