IDK bro if he has three jl subs wired in parallel, then it's gonna be fuckin loud. He's going to first of all need a good head unit. This is the cd or dvd or cassette player for anyone who doesn't know. Rockford makes an excellent amp. If you wanna go balls to the wall then i would go with PPI amps. They are top of the line but very expensive. 4K is a lot of money and if you're gonna spend it then do it right. Get some MB Quart speakers for the interior of the car. Make sure you don't cut corners as far as wiring and amp kits go. For 4k if spent properly you could build a very nice multimedia/stereo system. If you go to a res[ectable shop that sells quality products such as rockford fosgate, PPI, JL Audio, Focal, Alpine, Clarion, names like this, they will be able to tell you just what you need pretty much. You could build a nice system with like a TV and DVD player or playstation for 4k easily. Find out what you need and buy it on Ebay. Much cheaper that way.