After a lot of diagnosis, including bringing home a small faraday cage from work to test my setup in, the problem with my home studio noise problem is definitely EMI.
I tried the Electro-Harmonix hum debugger (crap), an Isolation Transformer on the line, and Ebtech Humm-x, various circuits, voodoo, witchcraft, and everything else you can think of. Had an electrician out, the power company came out, and I brought an oscilloscope home from work to try and pinpoint it.
I figured my only remaining option was to shield my entire studio, which would be expensive as hell.
That said, I figured "why not" and grabbed a basic ISP Decimator off Amazon for ~$125 or so. With it at the very front of my signal chain, it does a fucking FANTASTIC job of eliminating the EMI noise while not squashing the hell out of even extremely boosted tones.
I actually just bought another one (because I'm lazy) so that I can have one for the 6505 and the Axe-Fx. With the ISP in front of the II, I still run a soft noise gate and with the threshold around -50db on the ISP I am completely noise-free.
Awesome product is awesome. Get one.
The pedal? Or the rackmount?