Using a low to high convertor already ruined your "sound quality". Oh wait, the stock head-unit part already did. It will not be as good as RCAs straight from the back of a good hu. A Sony Xplod can get people to hear you coming fyi lol. The P3s and amplifier are a great choice for a first system that will give good sound. If you still want a sub good sound quality yet pounding, get a Image Dynamics IDMAX 12". If you want your lights to not dim, adding a new battery or replacing your existing battery is a great solution. I'm sure the G6 will have a good enough stock alt.