If you keep the stock resonator and muffler the sound stays civilized regardless of what else you change. The majority of power gains are from removing the cats. My advice is the NW cat delete downpipes and keep the rest stock. The NW downpipes bolt to the stock supports. You can remove them and go back to stock in around an hour if necessary. I installed them myself in a condominium basement on jack stands. First time took a lot longer but the second time an hour.

Les