hello
in the audiosurf map is a map called soundeffects.
all the sound there are in wav.
so in a state of total boredom i changed them, with all the sounds from unreal tournament 2003 demo (head shot XD)
and it worked

you have to name the new sounds the same as the old and they must be in .wav format.
here is my UT2003 pack, i did not changed the sounds for puzzle things like erase sound or shuffle sound.
http://rapidshare.com/files/103234499/chillout.zip.htmlput everything in the .zip in the chillout map in soundeffects (X:/program files/steam/steamapps/commen/audiosurf/soundeffects/chillout)
and make a backup of the chillout map if you want to reset it.
have fun.