If I may contribute, I knew my Onkyo TX-SR876 was going to run warm, and it lives behind the doors of a closed front, open backed cabinet.

From new in June 2009 ($1200), I installed an Antec A/V Cooler which sits right on top of the Onkyo. Fan speed is set to low, and it powers up when the receiver turns on.

It draws air from the top of the Onkyo into the Antec fans, then exhausts out the rear. Having the Antec running on low makes a noticeable difference in the temperature of the receiver. With the doors closed, the fan is inaudible to me.

The Antec A/V Cooler is sturdy enough to have another AV component stacked on top, and I suppose you could use more than one in an equipment stack. It is powered by a simple power pack, which I plugged into the switched power output on the receiver.

So far I have been quite happy with both the Onkyo and the Antec A/V Cooler unit.