adding a fan to an enclosed cabinet

Hello. I recently bought a cabinet to house my stereo equipment and sit my TV on top of it. I never had any real issues before with my amp getting too hot when I had it sitting on a rack that was not enclosed. Both my amp (Bryston) and HD cable box (Scientific Atlantic 8300?) get way too hot. What is the best solution for this other than leaving the cabinet doors open? My one thought was to add an exhaust fan (the type that would go on a computer case) to the back of the cabinet. Would I want to add an intake fan to circulate the air even more? The only ventilation that it has now is 3 1.5" wide openings running the height of the cabinet. Thanks!