I went ahead today and had a custom exhaust system split back behind the rear wheels, built and installed. I went with a Magnaflow "one-in, two-out" muffler, and had him keep one of the resonators (since it's a straight through one).

Sounds great, and I noticed a boost in power and torque. I drove it around a bit today, stepping on it of course to hear and feel it.

I also had him install a couple of Magnaflow chrome tips. Looks sharp. I might send in some pics here shortly.