Need Help: Export Audio Mixdown

I am trying to export a 16 track midi file by audio mixdown. No matter what I have done (by way of advice in the forum or operation manual) there is no sound. I would like to burn a CD, but have had no success. Can anyone help? Would be most grateful.

What is producing the sound?

Yamaha S90XS keyboard.

You will need to record the audio output of the keyboard into Cubase onto some Audio Tracks.