Nice title, BTW ... I came in here expecting nothing in general, had no idea whether I could even answer your question.
SNG is like a hardware midi, except much more advanced. There is apparently no direct way to convert any single dimension audio (like Mp3 or wav) back into sng.
You may be able to find something to convert something from mp3/wav to midi .. and maybe midi to SNG.
MP3->Wav is easy ->Winamp with discwriter plugin (standard plugin)
WAV to midi - http://www.pluto.dti.ne.jp/~araki/amazingmidi/
Midi to SNG - http://alchemist.sourceforge.net/news.html