2003 Nissan Xterra w/Rock.Fosgate factory system

i just had some questions regarding the rockford fosgate factory system in my 2003 xterra. i have read some forums of people with the same vehicle as me and making upgrades to the speakers and also adding a sub and amp. what i wanted to do was to put upgraded speakers into my car ie (Audiobahn 5.25 in speakers in the front doors and tweeters and either one 12" kicker comp sub or two 10" subs and an audiobahn 800wattRMS amp) while keeping the same rockford fosgate headunit. if anyone knows if this is possible or the pros and cons of it, it would help me a lot because i am not extremely knowledgeable in car audio.

thanks

http://www.automotiveforums.com/vbulletin/showthread.php?t=673317&highlight=nissan+fosgate

I posted a link to some hi/low converters also known as Line Out Converters that should allow you to install an aftermarket amplifier and still use your RF head unit.

waltman