Well, since you asked ....

``Appear'' usually refers to a physical manifestation. So, out of context, someone might think that ``music appearing'' might refer to the sheet music being delivered. But, in your context, I think we understand what you mean. And I can't come up with a drop-in replacement. The closest I can think of would be ``emanate'', but I think it would sound a little awkward without a qualifying adverbial phrase (that is, ``as soon as music emanates'' vs. ``as soon as music emanates from the empeg'' or ``from the speakers'').

This is certainly picking nits, though.