So when I figured out I was getting the X37 I did a bunch of reading on different threads about exhausts, intakes, etc. There were more than a few people making great power with stock cat back still and I remember reading one thread that was dyno'd with stock cat back then with a 2.5" exhaust and it made almost no difference. So I decided I would give up the very small HP increase to keep the comfort of the quiet ride. My tuner had no complaints and when I asked about upgrading to a cat back he said the same thing, it may make a small impact, but it shouldn't require any real re-tuning and my car was performing just fine on stock exhaust.
I also removed the Cobb Intake that was in the car for a RamAir filter, induction hose, and hopefully I'll be grabbing an ST200 intake box. I still get my share of intake noise with the charge pipes and the RamAir, but it's not loud and it's not overwhelming so I don't get all kinds of extra attention.
The Turbosmart wasn't really that loud either and it's adjustable, the sound was enjoyable for a bit, but I decided to try the other route.