I did the "crios mod" on mine a few years ago, and it made a nice change. A little deeper, and louder at low speed/low RPM. Above 3500rpm or so, and it's all induction noise anyways. You've pulled out your snorkel already, right?
DIY Exhaust Mod – Gain of 10+ HP!!!
^ btw, zero HP different here, it's just a silly title
I've got some cat bypass pipes I'm putting on next, to get a little more volume and rasp.