Did you have the stock Bose system?

 

idk if it was bose? but it did have the factory amp under the rear trunk

 

OK here is my opinion you should do the big 3 upgrade that will help the most with the dimming problem
I would look at a bigger alt at some point (if you are going to be adding to your system )
if you are looking at a Optima battery get the Yellow top it is made more for car stereo systems then the red top ( yellow can Handel the heavy draw of a system better ) I am running 1 yellow top and 2 kinetics

A extra battery does help a little but really helps when you are running the system when the car is off

and caps look cool but will not really help you at all because of there fast output they can actually put more of a draw on your battery than what your having now
I hope this helps

 

Yeah, those were factory-premium bose speakers you took out. I hope you kept them. Sell 'em the the ebay. Polks are nice, tho

 

yea i kept them just incase i do sell the monte at any time which i dont plan on lol...but the 4 new polk speakers i got are being powered by a alpine MPR300.4 amp giving each speaker 50 watts RMS at 4 ohms.... speakers SOUND GREAT but no dimming. once i finish up my sub box ill be throwing in 2 L5s and a kciker zx1000.1 amp to power them...the amps been collecting dust in my room nd its really been getting to me that i have no bass in the car bassically so i wana put em in soon! ill have pics of everything up once its done; just waitin for some better weather. i have a 720?ish cold crankin amp battery now and it helped the dimming situation i had wen i had 1 L5 and a kicker 400.1 amp powering it wen i had the stock battery...500ish CCA? all in all ive dumped 1 grand into this system for all the parts how much more am i gonna dump to get it to work properly lol