Does the audio not play when button is clicked in this case or is it the appearance of the audio which is an issue?
If you place a movie ... what's under the "Watch" text above ... there's no need to place the audio file for it separately. You just place the movie. The ereader puts its own controls on top of the move to play or pause it.
In addition, you can add a button that will play the movie. The user can tap the button. To do that, make or place the button artwork in your layout file, then convert it to a button in the Buttons & Forms panel. Then with the button selected, add an Action to the button: choose Play Movie drop down list of actions, and choose the filename for the movie from the list in the same panel.
All the same is true for Audio files. Users can tap the audio file to play/pause it, using the ereader's built in controls for audio files, and you can also make a button to play the audio, same as described for video.
A button can only play a movie or audio that's on the same spread as the button itself.
Does any of this info help? Are you trying to do something different than what I described?