Need super quiet exhaust fan

The quietest solution is to put the fan on the roof (one storey) or on an exterior side wall (if there are floors above you) and connect a duct to the equipment room ceiling.

Regardless how you decide to do it, you also need to think about where the makeup air is coming from. If it's coming under the equipment room door (undercut) it could have a lot of dust in it. Better to install a "transfer grill" and filter, in the door or interior partition wall of the equipment room.

Essentialaudio's details/tips are all good ones. You shouldn't need balancing dampers** unless you are exhausting more than one area, or have more than one return grill; in which case balance is achieved by adjusting the size(s) of the different intake registers relative to one another.

** Most externally mounted fan units are supplied with backflow dampers which close when the fan is off (to prevent cold air from entering ;-)