The alternative to using so many sources is to draw the readings mainly from a few textbooks/authors, which is certainly a valid approach. My own preference is to expose you to the broad range of original-source material that you would be expected to read if you were doing your own research in these areas. The best way of doing this right now is to use as much material as possible from the web, and make up a course packet for the rest.
If the publishing industry ever catches up with the most forward-looking
members of the
music industry, you will be able
to download individual articles for a reasonable fee.