I have som sony xplode 6x9s in my car and i was wondering how I can get more bass out of them because I don't want to put subs in my trunk because I need the space.
use an amplifier.. a head unit won't give the power you need to move the driver mass for decent bass response. get some better high power 2-way 6x9s or look at some 6x9 woofers (no tweeter so all it does is bass/midbass) and those solutions together may eliminate the need for a sub if you're not too demanding about bass response.
otherwise you're going to have to relent and add something like a small bass tube. you just can't get a lot of bass from speakers that aren't meant to function as subs in the first place.