First off, the bigger the speaker the more directive or focused the SPL is, this is how line array speaker systems work. The F factor in the line array is how close the drivers are. The closer multiple drivers are the more they act as one big driver. The port acts like a speaker but on a bandpass. I'm not trying to go into to much detail.
Also important know that the electricity in the car flows from the negative to the positive. That being say about the negative, what do you think is going to allow more power to flow, all the metal in your car or one run of 1/0? That's why it is so important to upgrade grounding around your battery and alternator to the cars body.
Batteries don't produce power they only store power, an alternator is the only way get more power. Don't bother adding a second battery unless you plan on running your system with the car off for extended time. A second battery will only cause extra stress on the alternator. Also Watts/Volts=Amps so 2000w/14.4volts= 138.8 amps, the stock alternator is only 105amps = dimming lights and stressed battery.
Check out my album
http://s215.photobucket.com/user/afugy/library/ I ran the speaker department for an audio company.