To have music start with a slideshow there's some post publishing editing needed of some of the .js files I believe. It's different than the file below I'm referring to. That's beyond my knowledge. Do a search for slideshow music and see what you find.
If you're trying to drag a audio track into a photo page it has to be outside the photo section. It can be up near the title with the control bar underneath and the top part of the object over the title area. Then select the title and send it to the front. If you want music to play automatically when that page is open see
this example. The file you want to edit will be title "site name.js' and will be located in the "site name_files" folder I suggest you follow the suggestion for the volume so as not to blow someone out who might have their volume turned up high.