You could also try disconnecting the cable TV connection.
It sounds like a ground loop or similar grounding problem. They can be a pain.
I think would start in one of two places. Either the new amp, or the whole system.
If the whole system, don't use the Power Bar and try just the main amp. See if you get a hum. Then connect something else and try that. Keep adding things on until you get the hum. That should help pinpoint where the problem is. It could be a bad cable, or faulty ground, or even mis-wired equipment.
The other way to start is by changing things with the new amp. Have you tried plugging it directly into the wall rather than through the Power Bar? Are the cables good? Does it hum only when you've got a cable connected to the input, or does it hum by itself?
Have you checked your wall socket to make sure things are ok? They have cheap testers (probably $10 or less) that you can plug in and find problems.
I moved into a new house a few years ago and went around testing outlets before getting settled in. I'd say that 1/3 of them were mis-wired or otherwise faulty.
Another thing to check is whether you have power cables running parallel to signal cables. The low-level signal cables can pick up hum from the power cables. If they have to be close together or touch, it's best if they meet perpendicularly. (That's not always easy to do...)
