Caveat, I don't know much of anything about the Krell stuff's operating parameters, but it sound to me like the amp is detecting too much DC output from the pre-amp and is shutting itself down. FWIW if it helps get you pointed in the right direction.
Help My Krell 700cx isn't working right.
I just recently bought a Krell FBP-700cx, after bringing it home and setting it up, a couple problems began to occur. If I played music past about 9 o'clock on the pre-amp, the system goes into protection and shuts to stand-by. And, a humming sound comes the speakers. I've tryed creating a new 20 amp circuit only for the Krell, but no luck so far. Can anyone help me?