I cut a slot out of the back of the entertainment center and put a large 120mm right above the area where the receiver heat sinks expelled the hot air. The fan was 110v that I got at radio shack (I think) and would turn on when the receiver did. You couldnt hear the fan when the system was on and the receiver ran cooler than ever... I would leave the door panel cracked open enough to draw in cool air and the fan pulled it right over the receiver and spit out the uber hot. Worked great. Check the air flow, does it pull cool air, maybe the size of the fan. Bigger is better, quieter and pulls more CFMs. Here is a perfect example of what you can get:
it has three 120mm fans. That should be WAY more than enough.
Good luck! Should take some pix so we can see the setup...