I cannot get my Macbook to stream to my airport express - no sound comes out

What I want to be able to do is to use DJay on my Macbook, and stream wirelessly to my Airport Express so that the music will play through my home stereo, which my airport express is connected to.

I see at the bottom of the app there is a little slider that seems to indicate that I have selected AirPlay for my chosen method of output.

Both the Macbook and the Airport Express are the most recent versions sold by Apple.

Am I doing something wrong, or is this actually not a capability of this app.

Note that I turned my iPhone, my iMac, and my iPad off just in case they were somehow interfering.

Right now all I can do is play songs through my macbook speakers and that is not what I want to do. ’

Please help.

Much appreciated,