Your best bet is to have a muffler shop install a Flowmaster, Magnaflow, etc. muffler to replace the giant sound insulating stock one. That will make the most difference.
You then have 3 resonators to play with the sound. One in front of the muffler and the two at the end. However, as mentioned, most people keep those resonators to avoid highway drone.
I went with a custom installed Flowmaster Outlaw, kept all the resonators in place, cost me $270 out the door and sounds great. Burly and mean around town, but no drone on the highway.