No, not everything passes in the Regression theorem. It has to be the most commonly used commodity to gain function as money, before that it was just another commodity, although popular. Bitcoin passes into money by the fact that you are using current money (fiat) to give value to the new money. Thus, from gold to FRN. from FRN to bitcoin. You can also buy bitcoin with gold.

It is the only theorem to be able to progress from commodity to currency on a real continuum, thus explaining money. I would say not very weak, at all.

In this case, music might be a non-scarce good, but the getting and storing and everything else connected to the delivery of music are scarce goods, there for can be priced in the market. And those scarce goods for the delivery of the music are rivalrous in the extreme.