Hello,
I went for a de-resinated mid section and wr sport backbox (thanks again bandit) on my 06 sti. This certainly brought out the burble, without giving me a sore head when driving. Looks pretty subtle too [Y] Not sure if you would get the same sound from a wrx, but I imagine it wouldn't be far off..
I made a short video clip of how it sounds now, bearing in mind that it sounded like a hairdryer before [:$]
hope this helps!