if you have any extra, just ground it with that.i alreaty have like 25 feet of 1/0 awg
i have 1/0 to a t block to two 4 ga with 4 ga grounds. all stinger.0 gauge is the secksy
i would run 0 gauge from the battery back to the trunk, and then run 0 gauge to your grounding point, and get 0,2,4 gauge distribution blocks for both, and run 4 gauge power and ground to the amp.
Then your already ready for your new equipment