do i need a capacitor?

Hey Guys, I am about to install a Rockford Fosgate 600watts amp with Boston Acoustics 8" sub in addition to my already installed Kenwood 600watts amp with Alpine Type-S speakers a in my 2007 Mazda 3 GT. I am also adding an Eonon GM5151 DVD/NAV system along with a Viper 5904 alarm system. Currently I only have the stock battery with stock wiring on my alternator. so my question is should I be doing a BIG 3 setup or getting a capacitor? Also, is there a way to hook up the kenwood and Rockford fosgate together? I don't want to run two positive wires from the battery all the way back to the trunk.

You don't need a capacitor - your system is too small - but you'd do the big 3 first anyhow. Two positive wires to the trunk is the as one larger wire to the trunk (in most cases - ie you may not want to mix inverters with PCs or audio). Use a big fuse at the battery/power end and split into 2 fused circuits at the back, probably via a distribution block.

Spark left out a bit of clarity (as I am reading it anyhow) (if it be due to my dense brain then ignore this). You need to add the max current draw of your amps together and compare that to the length and size of power wire you currently have. There are many guides available online that will tell you if your current wire can handle the demand you wish to put at the end of it. I agree that you should start with the big 3 anyways. To master and control electricity is perfection. *evil laugh*

Thanks RJ. I'm either too brief & cryptic else too verbose. My method for distribution design seems to differ from most of the industry. Whereas many design from wire (max) current tables, I design from raw data - namely cable resistance, max current, etc. That way I don't have to worry whether the wire tables are based on a max voltage drop of 3V (which - as a rule - many consider acceptable, but not me!) or fusing or safe temperature increases. Hence I decide max allowable voltage drop; determine or decide max current; then V=IR => R=V/I determines max resistance which must be higher than the cable resistance per length divided by its length. Of course connector resistances etc plus the ground path need to be included but that can usually be fudge factored or ignored. And confirm that chosen cables exceed wire table specs (which they always have in my experience where designed for max 0.5V or 1V drops). But all the above have been described before - including my BIG 4 (ie, Big-3 plus alternator +12V etc; or is that the Big-4+ ?).