I've looked at different mufflers online and have listened to the Audio for most of them.(thanks to a post in this forum) and have concluded that I could make the stock Muffler sound pretty good.
 Looking at the back of the muffler I didn't want to drill into the end of the baffle like others had done and have holes all over which to me would not look great so i came up with a different approach. I tappered the Exhuast port in with a cone shaped drill bit grind wheel then got my Punch set out and punch Four holes in the Inside of exhuast port using a 3/8 punch inside the pipe at an angle so the air would flow smoothly. Then used a rounded file to smooth out the burrs that my punch had made.  Started my bike up,   Holy Cow!! It Rumbles I mean RUMBLES like a Harley which in my opinion is awesome considering I paid nothing and it got rid of the rest of my backfire as an extra bonus.
So,if any one has a OEM Muffler mod that is better drop a post
           

Did you make any carb changes?

Hey thanks Scottwerty, excited to see a photo and possible  sound file. Going to make some mods on my S40 but just checking what kind of things like you have before doing anything.