The thing to be cognizant of, I think, is that CS/Business/Marketing at a University are already disconnected from the business world somewhat. The problems they solve are already more abstract and academic (in a good sense). So people are already negotiating the realities of business v. the academic analogs, etc. Music, on top of it all, is perhaps the most abstract field in the humanities (philosophy has systems of ideas, literature has words, the visual arts have images but music has predominantly...sounds?). That's not to say Oxford or any good university wouldn't provide you with invaluable habits and attitudes about learning for the rest of your life. But if you think about it as an investment, apart from what hiring managers will think, you're potentially exposing yourself to a pretty heavy load of abstraction. However, as long as you're aware of it, you can balance it with other things (organizing gigs as mentioned is a good idea), or do them later (or even while you're there -- sit in on CS lectures, read the books on your own, etc.).
