I used the Browse interface, just so I didn't have to lookup any FileKey's or do any Queries, just as a demo it can be done. Use which ever is easiest.Yup, the Action here is unnecessary for our purposes. You get an MPL with Browse.
If you use: http://localhost:52199/MCWS/v1/Library/Values?Field=LyricsYou'll get all your Lyrics, but no associated Filename. To get more Fields, you have to use the Filter parameter too.