I can't believe what i'm reading
. 6x9 are a Big no no in car audio circles. When you get a decent set of components and i mean decent and run off a powerful amp. You dont even a sub. Personally i couldn't live without sub bass in my sytem but with 6x9's you drag the sound backwards. Eg If you were at a concert, would you sit at the back and turn you back on the band??
If the system is setup correct, then the sub is balanced with the rest of the sound.
If your lights are dimming then you will need to sort out your cabling. Add some proper sized power and earth cable. No point adding alternators and batteries if your supply cables cant supply any more current. Sounds like its a fire waiting to happen
I have two different systems in my cars. 1 has expensive components and quality 10" sub in a sealed enclosure all runing off a single rockford Amp. The sound is very clean and clear.
The other is a two JBL amp system. One amp is 100w/ channel running some average components (which i am looking to change). The other amp is 600w RMS running a 12" sub in a ported box. This system is alot louder but not as clean because the components are cheaper. And not a rear speaker in site and def no 6x9's. This car has 0 gauge cables for battery earth and power for amps and the lights never dim even wen cranked up.