woofer can be install with pre. . .laikn kch faida nhn ho ga . . ..it will not produce any bass 
u must have amp to kick it . . go for mono amp with woofer . .if u r satisfied with your speaker vol and quality 
else you have to install 4 chnnl amp with nice pair of spkrz
but i must advce you to go for four spkrz and detcble woofer box
it need two amp mono and 4 chhnl
you must have budget arnd 20k for good system 