Seekbar and Layers

So, do you mean you are using the normal slide seek bar of the base layer as the audio seek bar? Or, do you have some kind of custom seek bar for your audio separate from the slide seek bar? Either way, you would probably need to place your audio on a top-level slide layer that remains visible the whole time you are on the slide. Set this layer to not hide other layers or disable base slide content. If you don't have a custom seek bar for the audio, you would need to make one with perhaps a slider and some JavaScript to index the audio clip, also on that layer. 

If you don't want to do any of that, you could always make a video file with only an audio stream. Then you can embed a video player on your layer, and use the built-in video player controls to scrub through the audio. Make your video solid white or black or whatever, and resize the player to hide most of the frame. The controls still fade in and out, but reappear if you hover over the area. you could frame it with a rectangle to help users find it