I'm pretty sure he won't pass. We haven't done any prep and while he is musical, he isn't Musical musical. He's very much a Grammar School Kid, but only tangentially a Music Kid.
However, I know I'd always regret it if he fails the 11+ and we hadn't at least tried. And if he does pass, his brother would get a sibling place, which means I could stop worrying about secondary schools full stop. Which would be nice.