The truth about getting "hot" is that some equipment is just plain and simple going to feel hot. It was how the item was designed to operate.
My Denon AVR 2805 sitting on a glass shelf in an open air rack system with more than adaquate space above the AVR until the next shelf will feel warm to the touch at idle. At full power, it gets a bit warmer. But the shelf above the unit is absorbing very little heat. In other words, the heat that is produced is being disappaited, not retained.
It is retained heat, or an excessive amount of heat that we must be concerned with.
Run the equipment in an open air space and establish a normal temperature for the item. And then run the item in the rack. If the temperature difference is not significant, then we have no worries.
As an example, let's say at idle your AVR's case is 92.5F in the open air space, and 116 at full rocking power. If the temperature is 94.0F in the rack at idle and 121 at full rocking power, you have very slight problem, that may still be within the tolerance for your equipment. However, if the temps were 112 at idle and 145 at full power, I would say it is time for some ventilation.