I have a 2004 Ford Explorer with the following:
08ZX750.1 amp
07DCVR122 Subs/Box
Pioneer DEH-P6800MP Stereo
Rockford Fosgate's RFK4X amplifier wiring kit
I'm just not sure how high to turn up the gain on the amp, I'm afraid of clipping, and ruining the equipment. It is currently putting out some bass, but I don't think its close to what can be done with this system.
Right now I beleive the gain is turned up past half way, but not quite 2/3's. Everything is broken in, I have had this equipment since April '09.
Gain by ear or here.
Gain by meter (You need some online calculators to figure out the exact AC voltage you are looking for, and I've not been totally impressed with the method - see discussion in second link above).
Hope This Helps!!!
2002 Ford Focus Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs