For maximum flexibility, something like a checkbox for every planet, and space platforms makes the most sense to me. So the user has the option to override any planet's music individually, as well as platforms. For myself, I'd probably enable it on platforms an nauvis only since I've heard that music for years now, and sometimes I do just sit on a platform and watch it fly. The new music on the new plants though I'm still enjoying.
It's your project though, and you're doing the work, so whatever you feel like implementing!