We stayed at Poly a couple weeks ago and we could actually hear the music pretty well from the beach. Several nights, we sat on the beach right in front of the Hawaii building and could hear the music.
I did find that you could hear it much better by grabbing one of the beach chairs and dragging it towards the back of the beach, right next to the sidewalk. If you get there early enough, you shouldn't have a problem getting a chair and doing this.