The fan should be put on a top of the Amplifier where is the hottest to suck the hot air out. Check this out. Many different options.
http://www.ebay.com/itm/AV-Cabinet-Home-Theater-Cooling-fans-w-digital-thermostat-multi-speed-contro...
http://www.ebay.com/itm/AV-Cabinet-Home-Theater-Cooling-fans-w-digital-thermostat-multi-speed-contro...