Lights dimming to bass... Options

[lilguy]

Hey all with my current audio setup when there is a high bass beat on each beat (doof of tha sub ) all the interior and headlight will dim slightly...

Currently have it set up:

Headunit (50x4 RMS)
powers: 6.5" 3-way speaker 55 watts RMS (back speakers)

600 watt 4chan amp (75x4 RMS at 4ohm, 100x4 RMS at 2ohm, 195x2 RMS bridged at 4ohm) powers: 6.5" component speaker splits 70 watts RMS (front speakers)
and 10" subwoofer 150 watts RMS (boot, through LPF)

900 watt monoblock amp (240 Watts RMS at 4ohm, 350 watts RMS at 2ohm)
powers: 12" subwoofer 250 watts RMS (boot)

Now doing a little reading and what i have gathered that will fix the problem is a Capacitor?
and from what i have read about them for ever 1000 watts of amps i need 1 farad.
So for my current install id be looking at 2 farads to be safe, but im also looking at getting another of the 900 watt monoblocks and the 12" sub to replace the 10" so that would be 3-4 Farads to be future proofed...

I have looked at some capacitors and they seem to be big $$$ and then some that are only $90-120 is there a difference in them, will they cause problems or are they the same basic thing?

Thanks all and if a capacitor isn't the solution what is?