I finally managed to get a line out from the Navigation unit that comes as an option in the crossfire.
for anyone that is interested here is what you need:

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN%3AIT&rd=1

it plugs in the back of the radio on the top plug all the way to the left.
it has 2 line outs, front and back but in this unit they are the same as their is no fader.
this plug also gives you a remote out which you need to turn on any external amps.

i wanted to install an aftermarket amp to the standard navigation unit, and keep everything looking stock and this allowed me to do it.
the cool thing is the sound still comes out of the standard amp.
so it is still powering the rear subs that come with the car.
and my aftermarket amp is powering the newly installed component woofers and tweeters in the doors.
sounds very good, but still interested in installing an Infinity Basslink sub in the trunk for added kick.

hope this info was useful for someone.