Get a white noise generator. I have an ancient one that sits in the corner of my office. It helps drown out the background chit chat and definitely helps me focus my attention without distraction. No one notices that is is on but if I ever turn it off you suddenly become aware of just how noisy everyone is, you can hear every sniffle and word spoken and you realize just how distracting that really is. Maybe stage such a demo, have your noise generator running for a couple of weeks, then one day when your boss is in your cube, just reach over casually and turn it off. When he suddenly becomes aware of all the distracting chit chat pouring in, point out how much more productive you have been since you got the white noise generator and how it serves the same purpose for you music used to do when it was allowed. It might open his mind a little. Or not. But the main thing is you can concentrate.