I honestly see it as unnecessary. I was going to do AH Music as well as my other subject last year (AH maths, physics, comp and crash H graphics), but decided against it pretty early on. I felt that what was timetabled it enough work, but not so much that you have to put too much effort into it.
If you're genuinely interested in the subject, and feel you're missing out, sure, go for it, but I feel that the 8 sg's/int's, 5 H's or 3 AH's + 1 H for each corresponding year is enough.