If you dont have enough of a capacitor in your system, either multiple or one really big one. That is the only way you will ever cure your headlights from dimming. Your stereo pulls a direct draw from wherever its hooked to when it romps them air waves. If you have it running through a capicitor the energy gets stored there and when the bass hits hard it pulls from the cap instead of the power source like a battery. The OE alternators are pretty good on the 7.3 psd's, unless you get a really good deal on aftermarket vs OE then I would say its not needed. I would say spend a hundred bucks or so and buy a nice capacitor so your headlights stop dimmin
also You dont need huge wattage to bump, Im runnin a mere 800 with a custom ported box and two p-1s and I hit at 137 DBs according to the guys at the stereo competition a few months back
. Its all about sound waves and tuning them to work in harmony with its enviroment! lol stereos are a science in there own!