There is not an authorized way to do this through Roll20 directly. But if the song is permitted on YouTube, you can use Google Hangouts to play the youtube for everyone at the same time. It's a workaround idea that wouldn't get Roll20 in a risk of copyright infringement: You can share a link to the music, to other people, in the chat, and they can visit the link in another tab. Perhaps you can find the music streaming on a legal royalty-paying site like YouTube, Rdio or Spotify. If it is on youtube, you can use Google Hangouts to have all the players start the youtube at the same time, so everyone hears the sounds at the same time.