Advice from someone who agrees with the idea of cooling the receiver, but NOT on spending $140 to get it done. I would get a 3" computer fan from a parts place or junk dealer. These usually run about $5, and they run on 12V. Next, buy a 9V plug in block converter that runs at a 9V or 10V output, with the amperage necessary to run the fan you have chosen. Most fans will have the voltage and amperage on a sticker on the hub of the fan. If the fan is rated at 12V, 0.2A, I'd run a 9V converter at 300mA or so. The reason to run the fan at less than specified voltage is to slow it down to make it quiet. Place the fan on one side of your receiver, likely the side closest to the transformer inside the unit (you say you have no room on top). This will serve to circulate the air around the unit so it doesn't let heat build up heat. You can plug the converter into one of your receivers switched outlets so it comes on only when your receiver is on.
Total cost - about $10 or less.