Has anyone considered placing a fan equipped laptop computer cooling pad under a power amp? Assuming the amp has underside vents, this could work. No doubt it may be best for the cooling pad not to actually bear the weight of the amp directly, so equipment feet could be used to give clearance.
This sort of thing: https://www.amazon.co.uk/TeckNet-Lap...F4KASD38BX1C0Z
They are designed to operate quietly and are probably quite effective as laptops can get pretty hot.