[burly]

One thing to remember if you buy your own is that you will want a non-polar or bipolar radial capacitor in order to wire it in series with the + lead of your speaker. Also, get one with a quality plate and electrolyte material and rated at at least 50Volts, preferably 100V. I use a pair of them on my front 4x6 component plates and it really helps free up the speakers to play frequencies that are in their dynamic range, instead of being distorted and overextended trying to play something below their range.

As far as speaker wire, I'm not sure I completely agree with the numbers being thrown around. Yes, a slightly lower AWG will probably improve your sound quality, but that is more due to the better RF insulation of the aftermarket wire than the OEM wire. Stranded 18AWG speaker wire is good for about 6-8amps at midband AC frequencies (~10amps for DC transmission or 1phase AC), and that is a rather conservative estimate. The resistance per 1000 feet is about 7 ohms, so in the 10-20foot runs in the car, you are looking at about 0.007ohms, negligible. With a 50W/ch amplifier, using ohms law a thats 2.5amps @ 20V w/ 8ohm load or 3.54amps @ 14.1V w/ 4ohm load. This is well within the capabilities of the wire and its given length. Granted, you wouldnt want to use it on your subs, but from a headunit to a speaker, 18AWG is sufficient with 16AWG being on the audio enthusiast side. Coming from a seperate standalone amplifier, it depends on the output wattage and the given length of the cable. The big thing in speaker cable, especially when running it in bundles of other wires in the car, looping and bending it around (introducing induction losses) is to go about 1 step lower in AWG (as in, 1 step larger wire) than the AWG rated for your power use, and blow the rest of your money on GOOD wires that have GOOD shielding. Power is only useful if it is clean.