Zimm,
Did you just cut a hole in the back and mount the fan blowing out? I have computer fans sitting around and saw a site that sells ac to 4 pin adapters for about 10 bucks.
Yep. I bought a 110v computer fan and plugged it into the switched power outlet on my AVR. Worked fantastic, kept it nice and cool. BUT...it was loud. For critical listening I would unplug the fan. If I was doing it again, I would pay extra to get an ultraquiet fan or multiple small fans. And with the amp behind doors with no fan, I promise you will wake up one morning and find you forgot to turn it off last night. I almost burned my house down as the Denon had heated the wood above it to the point I was sure a flame was next. I got the fan that day!