i have a 96 sc300

i'm about to replace the factory system, i was wondering of those that have done this, how you got the antenna to work with the new system, from diagrams i've seen, it has 3 signals: ant, ant a, ant b, are those the only siignals that the antenna receives, i'm guessing one is for reception and the others are for making it go up and down.. unless i am completely wrong

also, do the tweeters and mids in the door have separate wiring to the amp or is there a crossover in between the amp and the speakers?

oh yeah, also does anyone know how to interface the stock pioneer cd changer with a new head unit...
i got another pioneer head unit, but it's input is the ip-bus and i don't know if they'll match up

thanks again