Adjusting Audio Volume via UI Slider

So I've got four scenes set up, each with their own audios. For my coursework assignment we've to add a volume slider in the Options scene that affects all of the in game audios. I'm using the code from here to carry over the MainMenu audio to the Options and back, and then destroy upon entering the MainLevel, and will be implementing parts of the code to change the audio in the EndScene. The problem with the UI Slider in the Options scene is that it needs a run time object in the 'On Value Changed' component, and I can't add any of the audio objects from the other scene. Our lecturer told us we could use Legacy GUI, but the code he provided doesn't seem to work?? There's extra marks for using the UI Slider so I'd rather try and use that but I just can't figure it out :S