one thing, i though the GC8 alternator has around 90amps. and the wrx has 75 amps. thats what i was told at least. well im kinda having the same problem here. im running 2 12" 1000w RMS each bridged powere by a Lanzer 2000w amp( stated 1x2000w RMS bridged@ 2 ohm) so i probably running at 2000w RMS, which i doubt, but hey its close enough. anyway stock HU ans Stock speaker. also inside powering a PS2, LCD, and FM Modulator. when i have all those things on like to watch a movie or playing a game, my inverter beeps, stating votlage input is low. my light don dim that much only a fraction of a dim. oh runnign stock altneraot and battery. i was told my one of the member to change the altnetor or at least the battery.

 

I am running about 1500watts peak currently. Zapco 3.0 and 6.0
I have a deep cycle battery and a 5 farad cap.
My lights still dim, but my digital volt meter shows little to no dip in juice, even with the car turned off. (volume way up, hittin hard...)
Check out the Odyssey 1200 battery. They are small, light, and pack plenty of juice. Optima's are nice, but heavier.

-wrexr