i'd also look at where you are putting the sony amp...it needs a lot of air space. the circuitry they use overheats pretty quick...especially if it is powering subs at any ohm load below 4 ohms. I'd take RF over JL and a fosgate amp rated at 900w is gonna give a little more power than the Kenwood i seen you mentioned at 1000 w...the circuitry they use is an H class type...it switches to 2 different pipelines when the amp heats up...keeping it cooler over all. Cooler amp more constant power. And a capacitor stores energy until you need it...like during hard bass hits. It keeps the strain off the alternator.
Now with a capacitor make sure you have it wired correctly, i've been shocked by mine...it isn't pleasent... PS. i can back up the H class design because my amp is based on it..A Diamond Audio 1000 watt mono. i have it wired at 1 ohm and it doesn't get hot at all. My cap is a Boss cap but the trick with these are that they are representative. one company makes them..and a lot throw the badges on them.. BOSS, Stinger, fosgate, JL, and Tusami are all the same. Just pick which one you want.... SORRY FOR THE LONG POST I HOPE I HELPED YOU OUT