Camry Audio questions?

I have a 2005 Toyota Camry LE, and i recently put in a 900rms Kenwood amp two 12" Kicker CVR's and i think im running into current supply problems. I have a optima yellow top battery (which is less than 4 months old) with a stock alternator. Sometimes during very loud, low bass the voltage will drop to 11 volts sometimes even 10 volts for only a very short amount of time, then the bass will not hit as hard and it'll stable out at 12 volts. (btw the charging voltage is 13.5 volts)
(im planning on doing the big 3 upgrade later this week)

basically my question is: What is the output of the stock alternator? Do i NEED to get a high output alternator or would the big 3 upgrade be enough. And if i do need to get a high output alternator would any of you know a good place to get one at a decent price?

the reason im posting here instead of the audio section is because if anyone has done this kind of work before on their camry im wondering if you could share pictures or tips/tricks of how to wire or the wiring you've done for yours.

thanks!!

Do the big 3 upgrade and go from there.
13.5 volts is a little low, even for a car that has no audio system installed.
Voltage should be 14.5 or a bit higher.
If the "big 3 upgrade" sets the voltage at it's proper level, but it is still running out of current, then an alternator upgrade will be needed.
Or possibly a cap for the bass amp.

I may try the big 3 upgrade on my truck. It has a fairly powerful system in it and I tow a trailer from time to time.
I get a pretty good voltage drop at idle with everything turned on (lights, system, etc.).