oh yeah, yes you can ground your amp to the cap, provided the cap is properly grounded to the car. Also, keep your fuse for the power wire under the hood and relatively close to the battery. The fuse is to protect your car, NOT the amp. The amp has its own fuse to protect itself, but if the power wire ever got grounded to anything metal on the car and there is no fuse, then the power wire would heat up to the point of starting a fire in your car. So keep it within 18 inches of the battery and you will be fine. A 40 amp fuse should do the trick for that amp. Is it a class D amplifier??