Hi again..
Can’t speak for the Polk receiver though I know the Yamaha I have gets quite warm to touch when it's working.....
Having been a Computer tweaker for some time I appreciate and respect the fact that heat sinks do get hot though need to get the heat away to stay efficient and keep the components cool that should be.
Not all electronic componentry will complain straight up about heat though long term heat can cause the premature degradation of electronic components.
I’ve a similar cabinet to yourself and have installed a 120mm 4.7 inch in your language mains power fan in the back of my cabinet. I’ve fitted it with a light dimmer and it acts as a speed controller.
Watching HT I have the rpm/fan speed turned down so the fan is hardly audible, when cranking music I turn the fan up flat chat and it pulls masses amount of air from the cabinet..
At the end of the day, I sleep a little better at night.
Cheers and look after that investment!
Aaron