not strictly for an AV unit but I did something similar for my (closed door) server cupboard:

In and on by neilgates, on Flickr
2x 80mm inlet fans towards the front and 2x 80mm exhaust towards the back fans (to get air flowing into and out of the devices in the right places) powered from a HP Microserver.
flickr set: http://www.flickr.com/photos/neilgates/sets/72157633296476212/
dont know if that helps.

In and on by neilgates, on Flickr
2x 80mm inlet fans towards the front and 2x 80mm exhaust towards the back fans (to get air flowing into and out of the devices in the right places) powered from a HP Microserver.
flickr set: http://www.flickr.com/photos/neilgates/sets/72157633296476212/
dont know if that helps.