I was looking at the installation pdf file for a Borla exhaust, and found a picture of the stock exhaust for the 05/06 models. Looks like they have mufflers right before the tips at the back, in addition to the resonator right under the back of the transmission?
I'd suggest going a progressive route, and replace the back mufflers with something like Thrush chambered all-welded mufflers, which are about half the price of similar mufflers from Flowmaster or Magnaflow. Then, if the sound wasn't quite right, I'd remove the resonator next. 'Course another option that's already been mentioned is to replace the stock mufflers with glasspacks, but from my experience, 'packs don't last long and get too loud once the packing is blown out.