I have an Antec case, with a single 90mm fan in front, and a single 120mm fan at the rear, in typical locations. I have a Seasonic X-650 power supply. I'm changing over to a Noctua NH-C14 heatsink, although I'm not sure if I'm going to run 1 or 2 fans.
What case are you using?
you've got two 120mm exhaust fans (case, psu) but only a single 90mm intake fan. you're going to need a lot more intake if you want to match the two. and if you're sticking with just the 90mm intake, you're going to have to increase the volume quite a bit, i'd imagine.
have you measured your temperatures? unless they're really high, maybe this isn't a problem?