So I've recently acquired an ISP Decimator G-String and it seems to do its job pretty damn well well. However, it's also killing my sustain. I've also noticed that when palm muting with my hand on the bridge, the palm mutes ring out with very audible hiss. I don't know if anyone else has experienced this or know of any solutions. Should I invest in a second standard Decimator? Maybe even a compressor? Or should I be using the Decimator in the loop of the AMT SS-11B preamp? I would have thought it better to use it after the CAB...

I'm running my rig like this:

Parker Nitefly M -> ISP Guitar In -> ISP Guitar Out -> Tuner -> Boss SD-1 -> AMT SS-11B Preamp-> Torpedo CAB -> ISP Decimator In -> ISP Decimator Out -> Paradigm A2 Speakers

I've not got the gain set high on the preamp (10/11 o'clock), and I'm only using the SD-1 as a clean boost. I've got the Decimator's threshold set at 1 o'clock (about -25dB).
Guitars & Gear:
Parker Nitefly M
Sumer Metal Driver
Ibanez RGD2120Z
Two Notes Torpedo CAB
The G String is still only supposed to be in one loop. The Guitar in and out is like a "sensor loop" of sorts to better help the decimator loop with gating. It can't be used like an NS-2 to gate two separate loops effectively. Either use it in front of or after your preamp.
Gibson RD Silverburst w/ Lace Dissonant Aggressors (SOLD)
Electra Omega Prime Ceruse
Fender Franken-Jag Bass

Amps and the like:
Laney VH100R
Seismic Luke 2x12
Dunlop 105Q Wah
Gojira FX 808
Line 6 M9