HUM dilemma Can anyone solve This one?

Hi bob - read your posts on hum and hope you can help my dilemma. I have lexicon dc-1 preamp, krell kav250a, ead powermaster 500 and all b&w nautilus speakers. i have a continuous hum, as long as the amps are on. The preamp can be powered off, have satellite only, and if that wire is unscrewed from the wall, the hum is still there. Use a Monster HTS conditioner, all shielded interconnects, and everything is plugged into one outlet. Had three dimmers associated with the same circuit, and switched all of them for top-of-the line lutron dimmers (at $70/each!), switching every dimmer on the circuit. In fact, I ran everything by high grade extension cord to a different outlet on a different circuit - none of which changed a darn thing! The only thing that changes the tone of the hum is increasing or decreasing the degree of dimming on the dimmers - any of them. They are all grounded properly and have the latest RF suppression according to Lutron. The other difference I notice is that the speakers powered by the EAD Powermaster 500 tend to emit a slightly louder hum than the two mains attached to the krell. but when one listens, I still hear the hum in the mains as well. I will try cheater plugs, but dont want the expensive equipment at risk, but what else can i do? the last thing i should note is that i have six halogen bulbs in the dimmer switches, all of which hum similarly when dimmed. i am told this is acceptable, but the loudness of the dimmed bulbs is quite noticeable. Any ideas? This is a real dilemma for me! When sitting in the room with everything off (lights, preamp, tv, all lights, everything except the two amps [which are always powered on]), I still hear the hum! It's just audible enough that it makes sitting in what should be a quiet room kind of annoying. One last note - just to let you know I'm not crazy - even my girlfriend has noticed the hum and she doesn't know much about audio at all. She even jokes how her $200 system has less hum than my $25k system! Please help!!

In need,
Baz