Good news — I don't think you need to worry about this.
If you find a publisher, you will sign a contract. The contract might restrict your rights to offer the book and/or the music via your website, but only so that the publisher can offer it via their chosen means instead.
This is a good thing, because a reputable publisher will be better at promoting and distributing your work than you will be on your own.
The exact details of what you are allowed to do after signing a publishing contract will depend on what you negotiate (or your agent negotiates) with the publisher.
It's good to think about these processes, but you should cross that bridge when you come to it. The best thing you can do is to concentrate on finishing the book first!
One last note: Be careful about making your work freely available online. Copyright law varies from place to place, but in many countries, doing so will use up your 'first publication' rights, which can make publishers less interested in the work in question.
Hope that helps.