Exhaust system help for 00' firebird

hey everyone! i'm new here and I've been having a hard time figuring out what to do about making my exhaust system sound more deeper and aggressive. I have just got started getting into, and learning about modifications and upgrading cars since i just got a 2000 pontiac firebird for my graduationgift. Well, i have just a few mods right now, have a K&N air filter and a 80 series flowmaster cat-back exhaust system which i paid $275 for installation. I've had the exhaust system for a while now, i'm happy with it, but now I want to make the car sound more aggressive and with a deeper sound exhaust more like a v8 but i'm not sure what to do, I have a 2000 3.8L pontiac firebird. Should I look into buying a Magnaflow system?, i saw this one and was thinking it would sound better since it cost more but i'm no expert on this stuff!! http://www.magnaflow.com/02product/shopexd.asp?id=271, it was $512.
I was also thinking maybe I could just install headers and maybe that would increase the sound, I'm willing to pay up to $600 but your help would be greatly appreciated, thanks!!!

Welcome to the forum and sorry no one has answered you yet but I think the reason is this is the same exact subject as this thread http://www.automotiveforums.com/vbulletin/showthread.php?t=320374&page=1
So if you read this you should get plenty of opinions both good and bad.
John