To expand on what Ed said. If you check your manual, Onkyo gives some very precise recommendations for space above (8") and to the sides (8") and to the rear (4") as well as for creating a chimney effect to draw heat away.
A number of people with low clearance like yours have used this
fan with success. Used as a prepro only, with 5" above and 7" to the rear with closed front and open back, my 805 leveled off at 56°C after a couple of hours. according to the internal temp probes. The threshold to engage the internal fans is 69°C, but for peace of mind I cobbled together a couple of 140mm computer fans with a wall wart from RadioShack and placed them over the preamp section (rear half of unit) pulling air out to create some circulation over/around the video/audio processing chips that appear to be creating most of the heat.
Are you sure you interpreted that review correctly? Which review was it? I don't recall seeing any reviewers say anything like that and I think I've read all of the mainstream reviews of the 805. "Fail" sounds like an Audioholics review, but I skimming it, I don't see anything about degrading HDMI pass through. The give "film detail" a 0/10 "Fail", but plain "detail" gets a 10/10...I don't feel like looking up their test methodologies right now to understand the difference.
-Brent
