No, im no electrial expert so when times comes with those questions you might wana ask someone else but I do know that caps are useless!!
Your Volfenhag is doing 220wRMS x2 @ 4ohms and your JBL is doing 60w RMS x2 @ 4ohms, not a really power hnugry system
EDIT: Theres a section for this "Wiring, Electrical, and Installation Help" someone over there can recommend what to do, whether it be a distro-block/battery/alternator im not sure, sorry Im not an expert when it comes to this subject, but a cap is not needed i know that!
Ooo I must have been looking at the wrong model amp, your amp is rated at 600w RMS @ 4ohms, then its rated 800w RMS @ 2ohms, BUT your amp is not putting out that rated power, Volfenhag is a pretty LOW-end brand, cheap quality, most likely a lil bit overated with the power
see i was running these same 12's and amp in my nissan sentra.. but i was using 8 guage wire... i was using the pioneer def 4100 and a simple 1/2 din eq.. and i was hittin pretty hard..if i had my system on and i went inside the bank i could hear it..so i figured once i put the 4 guage wire, and reinstalled it with a new HU and without the EQ, that i'd be hittin real hard...
You're running your subs at 4 ohms, so you're amp is putting out about 500-600 watts. Another amp running 60x2 won't make a huge difference to your electrical system. If you have dimming, you can do a "Big 3" upgrade. It's cheap and effective. Do a search for it. Don't get a cap.
For speakers, the Pioneer Revs are a pretty good bet. Infinity, and Kicker are two other options that I like. Eclipse makes some very nice coaxles as well. You may be well served going to a store and auditioning several different speakers. We have no real way of knowing what will sound best to you. Personal taste is very subjective. There is no "best sounding" speaker.