Well now lets try and save you some money. You have 2 amps 1-600W and the other 1000W (most likely peak wattage, if that). You will find that most amps that have the wattage displayed on the casing are usually incorrect (but thats another story).

Understand of course, that no capacitor is a substitute for an adequate amplifier to provide the amount of bass energy you want to project. Nor will it substitute for an inadequate car power supply. You may have to install a stronger alternator if you have one of the more powerful systems.

A stiffening capacitor for your amp is the simplest way to be sure your system gets the immediate current it needs. A simple way of looking at it is by saying that you need a 1-Farad capacitor for every 1000W of power. Being that you are running less than 2000W, you should need 2 1-farad capacitors

Though your car may be pushing over 1000W (PEAK), you most likely would not need to go as far as to put in a higher output alternator.