Well nice head unit choice, they sound very nice
COmponets are definatly worth it, but before you commit you have to commit to an amp, most componets work best if you aim that at your head....
Now the crossovers assures that the tweeter dosen't try to play really low frequencys or the midbass try to play way to low of frequencys ect..... it gives them greater potential for getting loud and sounding good, and seperate speakers really helps big time because they can play different notes instead of playing 2 at one time, often the midbass is also stronger with a more detailed tweeter, theres nothing going through the midbass like wires either
I'm not sure I explained it good sorry, but trust me componets are the way to go, what ones are you looking at? what amp? I'd imagine you want some thing to compliment your nice Nak cd player