EQ, crossovers?

i have some advanced knowledge with EQing, but only on mixing boards, i was wonderin what the best way to do it for my car was?.......i have the pioneer deh-p3500.....a kenwood 800W......and 2 pioneer 12's (ts-w34c's).....and 4 pioneer 2 ways in kick panels and on my rear deck.......if someone could give step by step instructions, thatd be great........also imma replace my rear 2 ways with some 4 ways pretty soon here......will i have to EQ all over again?

Also ive heard crossovers are used for EQ too.....how/where are they installed, how much they cost, are they worth it.....etc??????

Matt

Crossovers used as EQ's?  Well... in a gross way, I guess.  By properly adjusting a crossover, a response peak where the performance curves from two drivers overlap can be minimized (like, say, adjusting the low pass for the sub to 90 Hz and the high pass for the mid-bass to 90 Hz and using an RTA to fine tune the two points so that the down slope from the sub and the up slope from the mid bass compensate for each other resulting in a relatively flat response at the xover point.)  So in a way I guess this is similar to the effect of an EQ.  But the two functions are not the same.

Similar to the useage of EQ in studio mixing equipment, connect your equalizer between your head unit line outs and your amps.  In your system description above you do not mention how you are powering your full range speakers.  If they are running off the head unit amps, you will not be able to easily add an EQ to them and are pretty much restricted to the bass/treble controls in the head unit preamp.

Also, yes, if you replace any component in your setup it will effect the system EQ and you'll want to adjust it again.

If you like the way they sound now using the head unit built in amps, why change it?

But, to answer your questions, if you have four speakers you'll want a four channel amp.  The power per channel depends on many things, but the generic answer is to find speakers you really like the sound of (which may indeed be the ones you have) and then match the amp to the speakers' power rating.  Buy the speakers first, and then get the proper amp.