Next/Prev buttons not working properly

I have a slide with a list of links the learner has to listen to. When they click a link, the associated layer shows with the audio file and when the audio file completes it automatically goes back to the base slide so the learner can select another audio file.

I had the Next/Prev buttons hidden specified on the base slide, until every link is visited. What happens is that on the final layer, instead of automatically going back to the base slide the Next/Prev buttons display on that layer. I do not want this to happen.

Then, on that layer I specified to hide the Next/Prev button so they won't show when the learner clicks the last audio link. Now, there is no Next/Prev button on the layer OR the base slide.

I want the last layer (S3 vs S4) to play the audio then automatically go back to the base slide where the Next/Prev buttons display.

File is attached and any help is greatly appreciated.