Thank you for the correction. I have not investigated capacitors in relation to re-enforcing car audio amplifier power supplies - car audio has not been my hobby for over a decade, I'm afraid. I specified a 2nd battery on an isolator circuit specifically to prevent the main car battery from being drained in the case that the person wanted to listen to the system with the engine turned off. It is a high powered system, and I feel that an isolated battery system is ideal in these cases.Chris... of all people I would have assumed you would have investigated capacitors. No need to waste your money... they do not help and there have been several credible tests completed that prove the same.
You can add a second battery, of which any would be superior than even a 100 farad cap. There is a company that actually make a product called BatCap (or something similar) that is actually a small battery for the purpose of extra power in a system. However, adding a battery is really only going to give you longer play time with the vehicle engine turned off. If you need more amps for the system, the only solution is adding a higher output alternator. I run right at 2000 watts in my car and use a Kinetik HC1800 (1900 Amps 81 Ah)... and I really need a HO alternator, but they don't make one for my vehicle at present.