If you like talking about music, talk about music. You should talk about whatever you want and whatever interests you, and talk about it with confidence and real interest in the subject. The girls will feel the interest and they'll become interested too. You should be the one leading the conversation so talk about what interests you. You can talk about science and philosophy as long as you don't make it sound boring.
But above all remember that it's not what you say, it's what you communicate. Like watabi said, focus mainly on your body language/sub-communication.
Hope that helps
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