Most places require a course of some type in music, though your instrument and theory grades absolutely do help, especially if you've been examined since they can count as UCAS points. You could look at doing a short level 3 course in music, but I would suggest emailing universities and asking about your circumstance first.
I've just finished a UAL level 3 diploma in music performance and production and received offers from all of my chosen unis due to getting distinctions both years, with my second year totalling to 168 UCAS points. I hadn't written about my instrument grades, as they're assessed in auditions (LCOM) , recordings (Hull) or simply not required (Huddersfield), so there's a variety of ways you may be asked to back yourself up.
It sounds like you would have a lot to write about for your personal statement, too. If a university says you don't need a music a-level / level 3 qualification, you'll have plenty to work with.