Randy:
I'm coming into this late, but can't you mount a fan in the closet and put it on a switch next to your rack?
A large fan running at a slow speed will move as much air as a small fan at a high speed, yet be virtually silent. If necessary, you can change the voltage to it (I don't remember how at the moment) to run it "slower than low".
I think moving some air in there, even gently, would likely do the trick. Blow the air from the back out through the front of the rack, and you'll help heat your basement in the winter!
My general thought is that a well designed amp chassis wouldn't need much more than a little help in moving the air a bit; the heat sinks would take care of the rest as long as the air is moving.
