Yes do the headers, I put ARH 2 inch headers with high flow cats and their 3 inch X pipe into the stock NPP and I love it! I did tune the car though after the install for best gains. I obviously did drive the car before the tune and had no issues. I picked up 37 RWHP with my exhaust install, however I don’t feel as though it was all the headers that gave me such a big gain. I feel the exhaust enhanced all the other mods that I have had done, but numbers are numbers the power can be felt in the seat.
Also even though you said you don’t want to void warranty I highly recommend the BMR engine mounts, they free up a TON of room.
Here is a link to how it sounds
https://youtu.be/E-MDIyLtV48