No iTunes speaker control pop up menu

I am trying to use an Airport Express to play iTunes through my stereo. I have the Airport Ex configured and recognized as a Network. I can hook up my stereo directly with a wire but I can't get it to play through iTunes. No speaker pop up menu appears when I start iTunes.
Any ideas?

Are all the updates for the Express and iTunes done?

Yes

I found it. I didn't realize you had to press a button at the bottom of the iTunes screen. It all works now. Thanks.