need alot of help

well ive been hooking up audio equipment for awhile now and i have a 89 camaro with 2 sony 12's and a 760 watt pineer amp i have 8 gauge wire in the car. which isnt that big of system.
but whenever i roll up to a stop sign or stop light with the radio/cdplayer on the car will die within a minute cuz it dains almost everything out of the battery.
i've upgraded to a bigger battery and ran a 8gauge wire from the alternater to the battery to help keep the battery charged more.
i've been thinking about buying a bigger alternator to help keep a better charge but i dont know if thats the right thing to do?