I currently have a 1200 amplifier connected in my car. I have two 4 gauge wires connected to my amp (One that connects to the red side of the front car battery and the other that connects to the black side).
What is the difference in quality from all 3 types of gauges?
Nearly nothing, nothing measurable at all. Your audio amp will never carry as much current as your jumper cables, and #6 jumper cables will carry the massive current it takes to start your car when the battery's nearly dead. If the power wire feeding your audio amp is larger than the wire running from your alternator to the battery to POWER that audio amp, then it's wasted copper - you can't pull more power than your alternator can supply without gradually draining your battery while you drive. Further, that one alternator wire carries power not only for your amp, but also for the headlights, taillights, heater blower, wiper motor, and ignition... plus any other extras your car might have (electric windows, etc). That ONE wire carries it all, so there's no need for anything bigger than that one wire.
I'm betting your alternator wire is a #8.
The basic differance between the differant thickness of cables is their resistance. A short thick cable has less resistance then a long thin one. Resistance in a cable causes heat. Heat causes melting of the cable, and may cause a fire. Once you know how many amps are going to be in the circuit, pick your cables by their rated ability to carry that amperage. To protect your vehicle electronics and electrical equipment, run ANY accessories on a supplementary circuit. This means taking a cable from the battery to an added in fusebox, and from the added fusebox to the accessories circuits.
