Indeed your unit is clearly "open air" so as your unit is running hot, an external fan is required to cool the unit down.
I'm simply saying that those owners experiencing high heat from their Denon AVR (regardless of model) doesn't mean that ALL units of that same model are experiencing the same heat issue and therefore a general characterization of "model XXXX runs hot" is not warranted. And although not obviously true in your case, in many cases, when more ventilation is provided, the temp of the unit should drop.
Mate, if you are a sales person or someone affiliated with Denon (or any other AVR companies) you should mention this here!
Calming down serious issues here and telling people there is no problem and deleting (my) posts about it is not the way a forum should be.