Caps do nothing but put a bandaid on the situation.... Your alternator still has to recharge something meaning that it's still going to be working pretty hard... Capacitors STORE power, they do not PRODUCE power. They still require to be "recharged" when drained by a heavy note being played. For example, you play a 5 second long 30 hz note, it will play for the first second MAYBE, but after that the lights will dim, and your typical problems will arise. I suggest you check in to a higher amperage alternator like a 200 amp or higher. Stinger makes some pretty good products and so does powermaster.
STINGER HIGH PERFORMANCE ALTERNATORS from STINGER HIGH PERFORMANCE CAR AUDIO ACCESSORIES | StreetPerformance.com
After looking at your avatar more closely, your problem is finding someone who makes a high amp alternator for an S197 mustang. I've seen 200+ amp alternators for a new edge, but no luck yet on an S197. There is a reason you see people with money compete in sound competitions, it takes some money to get competitive, unless you are just doing your local sound off which is usually an unlimited class with some who has 10 12's in an explorer with 10 amps... Don't know if that is your intent or not, but in all honesty it takes money to get a GOOD system running right.