How to fade audio in Keynote.....

Fading audio in not possible in Keynote, as of writing this.....but here is a workaround

1) Make sure Audio is playing across slides (automatically)

2) Fade out the visuals on your slide and add additional blank slides (x2) after the slide that you want to fade the audio -- with the audio ONLY continuing to play across the 2 blank slides, but lowering the volume on each successively -- 50% -> 25% (this way the slide appears to fade visually, and also audio wise as well.....)

3) Make sure to adjust the (automatic) Transition times between the slides to your liking (0.2s on first blank slide then 0.1s on the second is what worked for me).

This eliminates the need to edit the audio in a separate application, and also ensures that the timing is exactly right. Hope that this is helpful to the community.