Hum issue - driving me more crazy

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.

Bringing the cable above the floor may be moving them away from fluorescent ballasts. Speaking of lights, do you have any low voltage LED or decorative lighting that feeds off a DC transformer? These introduce DC into the wiring that get into ground loops.

To answer your question: yes, balanced IC's are the best way to go because the shields are tied to the chassis instead of signal ground. But somewhere, there is something that is amplifying your problem -- computers, improper CATV or Telco grounding, etc.

Elizabeth-> same IC. My cables are well and DOUBLE shielded.

Gs5556-> No fluorescent under the floor. No LED

Balanced appeals to me as best easiest possible solution. Should help with noise anyway

Now if I had only made the holes in the floor for the IC's bigger.... but who knew?

Can one build a balanced cable (for a trial anyway)?

If so one can someone tell me what to get at Altex or Frys or online. I can easily pull another cable behind the IC but balanced XLR connector will be problematic right now due to hole circumference.

Thanks to all for help, psychiatric consult, etc

In most cases, when components are all using the 3 prong cords, each component in the system has its own ground. Unless all of these grounds are routed back in the electrical system through one point, you get can a ground loop. This is because the components are also grounded by way of the ICs through the other components' ground as well.

If you are going to lift the ground (cheater plugs) try to do that on the preamp and let everything ground through the amps. This is how I get my amp and preamp to play nicely, but my pre has a switch for doing this. I do run a cheater on the QSC amp that runs my bass horns to eliminate a ground issue there.

If you haven't already, try to plug both amps into the same outlet and see if the hum is diminished. Matter of fact, you may need to plug everything in your system into one outlet to see if this helps even more. Use extension cords and/or power strips to get everything plugged into the same outlet and see what happens.

Interesting that you also have one side worse than the other. Try swapping the ICs between amps and see if the hum follows the change. It happens. Just last week I helped a customer with what turned out to be a bad IC, but in this case it was causing the input protection fuses to blow on his amp. Now that's a bad cable!

When you can, try turning off all of the breakers in the house except the one feeding your system and see what happens. This may tell you if the problem is coming in from outside.

Good luck! YOu have my sympathies. I don't think anything is as frustrating as finding solutions to ground issues.

You can probably remove the RCAs from the cables and replace them with XLRs. Most ICs have three wires inside anyway. If they do it's pretty simple if you can solder to attach XLR's. You don't even have to be able to solder with some of the new clamping XLR connectors.
Neutric solderless XLR