I have a pair of the MXR's. They are cool when in stand-by mode and only get warm when in active use. I have never seen them get hot. You can always place your full hand on top of them and keep it there. They sound great as well. I highly recommend them.
Ayre amps - cool running?
Can anybody with experience with Ayre amplification tell me how hot or cool they run? I've had a big Krell, which was very warm when on but no music, and downright hot when actively being used, and I've had big Simaudio monos which were cool when on but no music, and only slightly warm under most conditions.