During the Setup stage of installation, you are asked what filetypes to associate with Winamp
and whether you want it to maintain those associations.
You can manually change these settings later, by going to:
Winamp -> Prefs (Ctrl+P) -> File Types:
Deselect the file extensions you don’t want Winamp to be the default for,
and optionally, uncheck "Restore associations at Winamp startup"