Did anyone manage to ``repare'' a buzz, ever?

Thanks Sean for your reply. I actually tried all those things you mentioned (and some more) with the help of the comments I found in this forum. Even with everything completely disconnected except for a preamp, power amp plugged into the wall (or into the power conditioner) and just one interconnect between them (also tried different ICs, power cords, power amps) the buzz is stil there. It is not volume sensitive and does not go to the sub speaker when the 80hz crossover is engaged (but it is there if not). So, I am at the stage where I am seriously consider to go to a repair (Sorry Subaruguru) shop and wonder if this helped someone, ever.

I have had something like this happen from having cable music connected to my preamp. I was able to get some kind of gizmo that stopped it. If you have cable connected to your system this may be the cause.

Make sure the ground connection of your cable TV is clean and solid. Next, I would check if you have any halogen lamp dimmers and/or ceiling fan variable speed controls. These devices throw a huge amount of noise into AC power. If that fails, the repair shop may be the only option left, after you have isolated the problem component by deduction.
Good luck, I know this must be annoying.

It might not be your gear, but the room itself. Sometimes, if there are tracking lights present, or if any of the room's lighting is on a dimmer switch, that might be your problem.
I have that problem now - the lighting in my room is dimmer-switched, and it is wired to all the electrical sockets in my room (all my room's electricity is on one fuse). My preamp is significantly more buzz-y when the dimmer is set higher on the switch. Try taking your preamp to another room with a separate fuse/socket and plug it in. If you don't hear any more buzzing, it might be the lighting.

Is all your gear on one plug or circuit, meaning components on one circuit and amps on a seperate. If so, you may have a ground potential issue.(use an extention cord and test by plugging all devices and amps in same circuit) I am presently experinecing the same thing and found cheater worked on my pre-amp and amps, I basically lifted the ground..

Confused about the x-over issue, see if you can borrow the same preamp or another and test.

Matt