anyone have any experience with Krell Amps humming

Do you have the Krell plugged into an AC conditioner? If so, try
plugging it directly into the wall. Krell amps, like a lot of amps,
do not like to be plugged into an AC Conditioner and will hum
if plugged into one. Next, do you have all your gear plugged into
a 15 amp circuit that is not dedicated for your system? If so, your
amplifier may be starved for juice or picking up a hum from another
appliance in your home, or even from a neighbor's home. Way to
solve that is with dedicated properly grounded circuits with Hospital Grade outlets for your audio/visual gear. Put your amp
on a separate 20 amp circuit and a separate circuit for the AC Conditioner. If your AC Conditioner is also an isolator, you can
plug the rest of your gear into it. After installing dedicated circuits
all humming is gone, my system is dead quiet, sonics are improved and no more humming.

Your Krell is a theatre standard, I assume that's a mutli-channel amplifier. Does your Krell draw more juice than the other amplifiers you tried? And, do you have a powered sub-woofer?
Did you have a powered sub-woof plugged into the same circuit
when you tried the other amplifiers? Amplifiers and powered sub-
woofers draw a lot more juice than anything else in your system.
If your Amplifier draws more juice than the other amps you tried
and/or if you have a powered sub-woofer plugged in with the Krell, but you didn't with the other amplifiers, you don't have an apples to
apples comparison. It is curious that adding the Sub-woofer makes the hum worse.

You'll want to add a couple of dedicated circuits if your budget allows. I had humming problems and nothing worked until I installed dedicated circuits -- now it is stone silent -- no more humming of any kind. One other thing -- I did specify 10 gauge wire for the 20 amp circuits. Please write in and report after you get the pins and dedicated circuits -- I want to hear a success story!