YASAPI NT's 2.0.0-beta3 release consists of

* "out_yasapi-nt2.0.0-beta3-msc.exe":  the plug-in "out_yasapi-nt.dll"
  compiled with a community edition of the Microsoft C compiler and
  wrapped into an NSIS installer,
* "out_yasapi-nt2.0.0-beta3-msc.7z":  the plug-in "out_yasapi-nt.dll"
  compiled with a community edition of the Microsoft C compiler and
  packed into a 7z archive which has to be unpacked and the plug-in
  copied to the directory "<Winamp root>/Plugins",
* "out_yasapi-nt2.0.0-beta3-gcc.exe":  the plug-in "out_yasapi-nt.dll"
  compiled with an MINGW edition of the GNU C compiler and wrapped into
  an NSIS installer,
* "out_yasapi-nt2.0.0-beta3-gcc.7z":  the plug-in "out_yasapi-nt.dll"
  compiled with an MINGW edition of the GNU C compiler and packed into
  a 7z archive which has to be unpacked and the plug-in copied to the
  directory "<Winamp root>/Plugins",
* "out_yasapi-nt2.0.0-beta3-src.tar.gz":  the plug-in's source code, 
* "README":  this README file.

Beyond that you'll need a GTK runtime for Winamp you might download from

    https://sourceforge.net/projects/yagtk-rt/files/