First, be careful aiming a fan at Any piece of gear. IF you are somehow interfering with the natural convection (hot air rising) currents that the heating of the piece causes, you could actually make it run hotter, or too hot.
Premium (read as HEAVY) power amps like the Krell should be able to take any power demands in stride. Especially when used in an open installation. The Krell 300 or 400 integrated is a possible exception. My brief exposure to one (the 400) showed it to run bigtime hot. For my confined rackspace, that was a deal breaker. The Stereophile test confirmed my impression when they remarked on the heat of the amp after the pre-conditioning period before bench measurements, Worse Case Scenario, to be sure.
How much are you asking of these amps? I don't see how you should be able to put a dent in 'em....... If they have not gone into thermal protection then there is probably nothing to worry about.