okay, since today I was so eager to run some wiring and set stuff up, since I don't know how to work with 4ga wire (tools-wise), and since it's too short (only comes out the firewall about 2 feet, with about 3 feet in the trunk), I just wired one 8ga power wire.
Right now I only have that one 4 channel amp. I'm thinking about all this stuff now in case I decide to do something for rear fill - in that case, I'll use the 4 channel for the front stage and rear fill, then get a separate amp for the sub.
never knew how thick 4ga was...but to me it seems like overkill for my [planned] system. I was lookin at the back of that kit and it was like @16 feet and total continuous power @ 600 Watts, I should use the 8ga kit. So I'd never need that 4ga wire (but the other stuff that came with it were very helpful). (I'm an sq, very-minimal-volume-outside-the-car-with-windows-up type person).