Ok guys here is the thing i have a power cap for my amplifier to power my subwoofer and i am running all my power wire and ground for the amp and ground for the power cap all that is 4 gauge and I want to hook up another amp so is it possible for me to use 8 gauge from the power cap to my second amp and ground my second amp with 8 gauge because 4 gauges is simply too big for my second amp that is gonna power my 2 6x9's so that is my question thanks for your input.

Yes, you can use 8 gauge and wire it how you have indicated.

thanks for your help