well a rheobus should serve you very well with all those fans

id get a new fan for that heatsink
even an adaptor to use a 92mm fan on that 60mm size heatsink if such adaptor exists

btw i think you have too many intake fans for your case
PSU and 1 rear are the only exhausts fans right?
maybe unplug one of the 120mm on the side as suggested by james

is most of the noise coming from your PSU, HSF, case fans, hdd or cdrom?

watercooling is a good way to go since you have a case of that size
but a bit pricey than just some simple fixes that may make the sound level a bit better