I had some success making my scooter sound nice. The muffler on it is some kind of aftermarket fit anything sort of thing I picked up locally (in Aust). It came with a glasspak perforated tube sort of baffle which sounds really cool but is just too darn loud. I took it out, cut the end caps off and welded them onto a tube the same length as the original (so it fits back in nicely). Cut a slot most of the way through the tube halfway along and inserted and welded a blanking disc in there. So now theres 2 chambers in the tube. Then just drilled holes in each chamber and tried it in the muffler. Kept drilling holes until the power came back and it had a nice note, but stopped before it got too loud. It sounds good now and while it won't pass a roadworthy, at least it shouldn't attract that kind of attention anymore.
I went with this muffler because it was available locally, I think it looks better than a Dyna muffler and the Dyna mufflers aren't easy to get SH here. Everyone hangs onto them in case they need to attend a roadworthy themselves .
The tube on top is the original glasspak tube. The blueing on the muffler is from a previous baffle I made to get it through the roadworthy. Really cooked that chrome.