Amps aren't just for "oomph"...they also do wonders for sound quality.
My cousin and I installed 2 sets of Infinity Kappa Perfect 6.1 component speakers with a 4-channel Alpine V12 amp and Alpine CDA-7995 in his GTI. I must say, it sounds fawkin' sweet!
I myself have the Alpine CDA-7995, an older 5-channel Alpine V12 amp, and one set of Infinity Kappa 6.5 component speakers in the front, and 2-way Infinity Kappa 6.5" speakers for my rear. Mine also sounds good, but not as clear as my cousins because I got a "professional" to install mine rather than do it myself, so it's not as good an install...plus, my speakers are the older green Kappas and not the new silver Kappa Perfects.