Hum issue - driving me more crazy

Connect the A/C grounds along the same path the pre to amps interconnect goes. if it fixes the problem you can leave it that way permanently.
Even try the the neutral line same way. (but do not leave it, if it 'fixes' the problem, then you need to do some A/C rewiring) just leave the hot wire alone.
Sometimes electricians use the neutral wire in wrong ways and connect it up to other stuff instead of a pure separate wire. just the neutral A/C wire. (My refrigerator circuit neutral is connected to my separate 20 amp circuit neutral. Grrrr. But it does not seem to be a problem for me.)
Other possibilities: one of the items is wire wrong internally? hot and ground reversed?
Then also: run extension cords from ONE outlet at the preamp to both amps to test for buzz. If gone, then it is the A/C wires to that side are somehow currupted. IF no change with the extension cord, then it is not the A/C wire.

A comment about dimmers: some are great, and some are 'dimmer from hell'. I had one dimmer that would burn out bulbs in less than a two months. All the time. then another that the bulbs last for YEARS. same usage.
My understanding is some cut the current wave vertically and completely slicing it, bad lots of RF, some horizontally with a hard cut, OK, and some horizontally with a soft cut, (probably they just add a resistor, or a cap in the thing) and those are good, not so much hash.
None of them tell you what type they are. just from replacing bulbs you may know which are the bad type, as they kill bulbs faster. I took the good ones with me when I last moved!! (four years for the bulbs in the one room with the 'perfect' dimmer, and I use them every day!!)
Finally with your stuff you should get a pair of 14B-SST2 for those 4B-ST.(even 2 of the 4B-SST2 used would be great)
I have a 4B-SST2 with my 3.6s and it is really good. (I almost bought an ARC REF 3 used, but bought a Bryston BP-26 preamp.
Anyway, I like your stuff, and have similar stuff, so i 'more than usual' wish you well.
Good luck!

But there is constant low level hum - right side only EVEN with preamp and XOVER turned off.

I agree with Gs5556. Try some ground cheaters.

Just because you turned off the preamp and xover that would not break the ground loop current path through the right channel amp.

Have you tried to isolate the right channel amp from all other equipment? Nothing connected to the input of the amp... That would tell you if the low level hum is caused by the amp or not.

One other thing to do, swap the amps. leave everything else the same and swap them. If it follows the amp, time for a repair.

Page 2 (Continued)
I have used cheaters in all possible combinations with resolution of most of the hum BUT not the residual in the right channel only.

I have disconnected the dimmers from the circuits in room->no help
Reversing amps and XOVER outputs -> no help
Ground lift change on amps->no help
Preamap powered off and XOVER powered off -> no help
Electrician has reevaluated wiring and says all is OK
Separate 20 amp circuit has its own ground
No lights are plugged into stereo circuit

Unplug interconnect at right amp -> RESOLVES HUM
" " " RIGHT XOVER OUT -> RESOLVES HUM

Bringing the IC to the right amp TO ABOVE the floor-> RESOLVES NOISE. In my unknowing frog brain, this implies something is inducing noise in the right sided IC (when under the floor - down about 12-16" is all though). But nothing can be identified so far

As I know not enough about electronics:
Unplugging or turning off preamp or XOVER does not help - > are these eliminated as issues causing ground loops etc when OFF? Or are they still part of a system with potential "current flowing" (even though "off")

Does disconnecting IC from AMP (or at XOVER) TELL SOMEONE WASSUP?

Perhaps, as a (sort of) simple solution - > Would balanced from XOVER to AMP resolve the issue regardless of cause?

Thanks

When you say you bring IC to above floor, the same IC?
Or just another one.
I will assume you actually bring the same physical interconnect up.
Then you have some wierd stuff in the floor.
Something is causing a field of some kind in there under the floor. Could be even something in ground under the house?

A way to cut the field would be to run a armoured cable sheath (like used for A/C armoured wires) and run that under the floor with the interconnect inside. and ground that shield to the A/c ground.
that would cost about a buck a foot.
If that did not work, or only partially then:
Then if you can use a balanced connection, you should. A balanced connection will (Hopefully) not be affected by that.
I would see if you can borrow a suitable cable from a cable place or your dealer, and try it, Even if you can borrow several shorter ones and chain them together just to try out if it cuts the hum. Then you can buy a correct one if it works.
Then even both the armoured cable shield ,and the balanced wire.
If you use it for one channel, and it works, i would do it for both (the balanced wires).

No guarantee.. but other stuff to try
Also: Non contact voltage detector: From Amazon: Greenlee GT-16 ($22) it goes off if a electomagnetic field is around, or something is spewing out a field. IF you can actually get under (a basment? or crawlspace?) and use the detector and it will go off if a field is present. it may be just in one spot. Or a big area.
http://www.amazon.com/Greenlee-GT-16-Adjustable-Non-Contact-Detector/dp/B001QIJOW0/ref=sr_1_1?ie=UTF8&s=hi&qid=1306389698&sr=8-1
Well worth checking out.