The four sound files that make the crowd sound effects when matches go off can be found at:
www.bestgameever.com/crowdsounds.zipTo put em into your sound effects, go to the engine\sound effects folder of Audiosurf (navigate to Audiosurf in steam\steamapps\common).
Then copy one of those file folders that's currently in there (chimes for example) and rename it something like chimesoriginal. Then into the folder that's named "chimes", copy over these four files in place of the ones that are in there. Then whenever you select "chimes" in the sound effects, the crowd sound effects are the ones that will go off.
You could go wild with this and make whatever sound effects you wanted just to see what works. I did the best I could with it but am always looking for more cool sound effects schemes.