X-Pipe Resonator Delete fulfilled the exhaust sound I was looking for. I couldn't imagine my 350 being any louder than it is.
Lethal Performance X-Pipe. I think it's manufactured by Stainless Works.
Good luck on your exhaust journey.
I have driven both. I prefer the 350, it's just more raw. The M is a great vehicle too if you like a BMW. It's more of a comfortable street car IMO, but I'm sure it does well on a track too.