if u wanted the deep note a wrx makes then u'll have to go with a cat-back. axlebacks wont make much difference in sound. but just to let u know, u'll never get the same exact sound. diff engine, turbo etc etc. heres the megan racing cat-back that was on my car:
http://www.youtube.com/watch?v=9YdKS74k_Y4
its really dark and bad vid quality. but thats pretty much how it sounded. its the exhaust i still have lying around.