I think the important thing in a Car Audio system is the wiring.
Rule of thumb for a decent sub,amp and component system.
16 gauge to 12 gauge for speakers
8 gauge or 4 gauge for power cable with a minimum of 80A fuse.Mostly people use 4 gauge.
Rewire the whole system if you can spend some money.Power carrying cables on one side of the chassis and the speaker cable on the other side.
Keep the cable length to minimum
Bigger Gauge number - Cheaper,carries less current ,thinner.
Smaller Gauge number - Expensive,Carries more current,thickness increases.