I asked the same question a while back. The guys told me the ISP Decimator pedal was the one to go with. I haven't gotten around to getting it yet though.
I have a Digitech GSP1101 connected via 4CM, with an engaged gate. It can be set to engage before the preamp OR in the FX loop. I can't remember where I have it set right now, but it silences the hiss pretty well.
I get hum on all channels but most noticeable on channel 3 when I have it hooked up through my rg16 when my roadster is also hooked up. I've tracked it down to a ground loop due to the roadster. I know it is a ground loop due to the roadster because if I lift the ground on the roadster (experiment only wouldn't play with it lifted) the hum goes away. To resolve this safely I'll be getting a power isolation transform that can handle the roadster's wattage. To figure out if the humming is due to a ground loop or noise coming from a poorly shielded cable or guitar, you'll need to start unplugging things one by one to isolate the component.