Attempting to add soft music to all layers

Hello everyone!  I'm trying to think of the best method to add an additional sound layer to my entire project.  My purpose is to give the video, which is used as a software demonstration, a bit of pep!  We have a Narrators voice on all the slides already that is taking up the slide sound layer, so I would need to add this soft music into the sound properties of a hidden object.  Now, I can easily see how this would be done, but I don't know how you would eliminate the sound jumping from one slide to the next.  You can't edit audio from one slide to the next unless it is the primary sound layer.

Do you think I need to look into different software for this?

Thanks,

Jeff