the tuning kit from langtuning got 6 PS with AOA1. u take the original exhaust and modify it. its quite simple.
there is a sputnik tuning kit for s50 engines as well
http://zweirad-steinberg.de/sputnik.php its the s63 kit...
greets
*edit* langtuning got a very good reputation, sputnik from steinberg is good as well but i have a friend who had some trouble adjusting the carburator in the beginning but runs fine as well now