It sounds to me like the m3 mod is just cutting out the internal silencer and replacing it with a straight pipe. I wonder how different this would sound on a 335i doing a straight pipe internally vs doing a muffler delete. The difference would be that there would still be a connecting pipe between the two mufflers and there would still be a flap. I can't load the pic from my phone but search "335i exhaust cut open" in google images, there is an image that will make this make sense. It would be awesome if someone would try it to see how close it sounds to the PE.
2010 335i AW e90 Msport