I had been meaning to answer your question earlier - my Onkyo never seems to get hot. I like concert films and movies a bit louder than my wife and son, but I've never measured the dB produced.

My Harman Kardon in the living room, powering (ahem) a set of 5 BOSE Lifestyle cubes and "subwoofer" actually gets much warmer from less spirited use.

Bears, beets, Battlestar Galactica.