big 3 or h/o alternator?

hello people. i have a 1993 camry. i have stock electrical. im having alot of dimming and voltage drops. when i first blast my music, the bass sounds loud and good but a couple seconds the bass decreases. and my lights inside the car dim like crazy also my headlights. what should i do first? big 3 or h/o alt.? right now im running a 4 gauge wire to from my battery to the amps (4 gauge to the mono amp and 8 gauge for my 4-channel amp using a distro. block). if alt. needed, i appreciate if you can give me a good brand and tell how many amps should it have. my mono amp's fuse rating is 80 and my 4 channel amp's fuse rating is 40. so that is a 120 total its pulling from my stock alt. which my stock alt. is about 70-80 amps.

You should do the big 3 first. You need to do it anyways if you do upgrade your alternator. Your stock wiring is not going to be made to handle the higher current.

personally id say first do the big 3, drop a few bills for some 0 gauge, you will notice a small difference, secondly get better battery, higher cranking amps are better, agm batteries are good too, id do the alternator last because the alty cant instantly give off enough power for a series of heavy bass hits without a battery to back it up