FWIW, re cooling:
Usually the manufacturers require ~6-8” all around the AVR for adequate cooling. If it is in a Cubby, this exacerbates cooling.
Depending on your circumstances, I would readily recommend some sort of cooling scenario, but your needs will be dictated by your setup.
If your AVR is getting overly warm, then you need to be able to pull clean air through, and vent hot air away from, your unit.