Why put a fan at the front if you have two exhaust fans? Several questions need to be considered. Overclocking? Where is the air that is being exhausted coming from? Are those sources sufficient without getting a boost from a fan? Key is what are your inside-case temperatures? If they are reasonably close to room temps and you aren't oc'ing, you don't need an extra fan likely. Modding the case will take time. It may be cheaper (given manpower spent on modding) to get a temp sensor (e.g. Digital Doc 5) and find out for sure, unless you want to fool with the case. You didn't say whether there was a spot in front to mount another fan, and the spec page you gave indicated only one extra fan. You named two, so I presume the exhaust fan you mentioned is a slot-mounted fan, usually 43 cfm and very quiet for the cfm rating.
Think about what the air flow within the case likely is now and what it would be if you added a fan at X location.