The muffler mod involves cutting the back cap off, and removing/drilling holes thru the various baffles inside, then rewelding the cap. I also removed the silencer tip in mine, the part youo can see inside the end with all the little holes in it. Really opens up the exhaust flow, sounds pretty good if done right, and will hold up way better in the mud and water than the aftermarket mufflers that use a glasspack system. Helps with flow enough that I needed to jet up a couple sizes when I did mine. Cons are that it's technically illegal to modify your exhaust, issues with spark arrestors, sound levels, etc.
Yeah was gonna, but this was free, and never needs to be repacked after burning out from being submerged and packed full of skeg too much.
Not sure on the brutes, but years ago when the 650 first came out, there was a guy in Nova Scotia did dyno testing, and found the modded stock pipe made as much or more power than his aftermarket pipe, pro circuit I think, there wasn't many available at that time.