I recently had to install a glass door on the front of my 4.6 cubic feet (internal volume) AV cabinet because my 1 year old son started walking, and the components are all well within his reach. It is worth noting that i drilled several evenly spaced 1" holes on the individual shelves based on where the component sits on the shelf, they are not visible with the components in place. Drilling the holes was crucial in my case, as there was zero room for air to move between shelves, so a fan mounted in the center would have only been effective on the AVR (see diagram below). I really hope this helps someone out there with a similar problem. I will try and find the time to upload photos, but like I said, I have a one year old at the house to keep me plenty busy.
Here is a simple diagram of where everything is positioned, my apologies for the lack of pictures...
(IR=IR receiver for the harmony one to control the PS3, H1=harmony one charging base)
This is a table of measured temps in degrees F, before the fan (ambient 75 deg F)...
Fan was installed dead center in the rear of the cabinet, being used as an exhaust fan, measured temperatures after the fan (ambient 75 deg F)...
During temperature testing, all components were on, volume at -24db.
The on board temperature readout from the 609 was 4-5 degrees higher than the temperatures I measured externally before the fan, and after the fan was lower than the temperatures I measured externally by 4-5 degrees F, so the on board measurement before was about 135 deg f before the fan, and 95 deg f after the fan, a 40 deg f drop
I purchased the fan from coolerguys, and it is plugged in to the usb port on the back of the DVR. The fan is about as close to silent as it gets, the only time i can hear it is if everything is muted and nothing in the house is making any noise, AND I have to be standing within about 5 feet.
I did not expect the fan to work this well, I was expecting to have to buy at least one more, but this single fan is more than sufficient for my AV cabinet of roughly 4.6 cubic feet, $30 well spent I'd say.
I hope this helps somebody out there.