Another vote for: move the CPU out of the tracking room!
You can spend lots of time and money replacing stuff and still you have something in your studio that will make some noise. Then what?
I gave up and moved the CPU out into the adjoining room and ran the cables under the doorway. Going through the wall was not an option: all the walls are 8" of concrete or thicker. All the cables are carefully dressed under the carpet, through the doorway on the floor and over to the back of the CPU about 1 foot away. I have double, sealed doors into the studio. The outer door is hollow steel, the inner door is solid core wood, and both seal all around to the metal clad, concrete threshold, so even the doorway drops the noise by at least 40 dB, if not more.
Cost me $12 for a monitor extension cable and $30 for a USB extension cable. I'll probably also spend $15 for an extension cable for the Delta 66 so I can have a little more flexibility in placing that unit.
Now, it's once again quiet enough that the power supply on my Casio MIDI keyboard seems loud.
One sacrifice is that I now face away from the monitor speakers to face the computer monitor, keyboard, VU meters, patch bay, interface, etc. Of course, the plus side to this is that the sound at the monitoring spot is much better because there's nothing in the way causing reflections or messing up the stereo image.
ofajen