I want to add a sub to my vehicle and it has a dual voice coil subwoofer. It has four wires feeding the subwoofer. Do I need to use all four wires or can I only use two. Wiring says channel A +- and channel B+-. Never seen a situation where two separate channels are fed to one speaker. Not sure if I need a dvc sub or if I can use a svc off only one of the channels. Thanks.