Ideally, the amp should be placed with nothing like a cabinet around it, but if ambient temperatures don't exceed 30 Celsius, there should not be a problem.

And in the cabinet, pull the amp all the way to the open front to allow the heat to escape the cabinet quicker.

Mine reaches 43° Celsius.
I think the airflow is more than sufficient.
After all the Amp is supposed to be stackable!

 

Sonos suggests an operating ambient temp range up to 40 Celsius for the amp.

I don't see 40 Celsius ambient inside my home even in the hottest months in India. Without any aircon running.

 Ok. Well, if  40°Celsius ambient is a safe temperature for the Amp to work in, than  maybe  I shouldn't be worried too much

Thank you.