With a stock header I would just run a el-cheapo turbo muffler and a 2" pipe that you can get from any muffler shop. That's what I did on the X-90 and it sounds perty good and not to loud. I have the Calmini header, flowmaster muffler and 2 1/4 pipe on the Kick. I realy like how it sounds, but without the Calmini header it sounds completely different (had on on the X and took it off)
Zig