Dude, there are loads of third-party music apps out there, including plenty that let you copy music to your phone any way you please—from a USB drive, from SFTP

Dude, there are loads of third-party music apps out there, including plenty that let you copy music to your phone any way you please—from a USB drive, from SFTP, etc. Check out nPlayer for a power-user media player. Personally I keep my personal music in Plex, and my Plex server is available to me at any time. I can locally sync whatever music I like. I’d gladly use iCloud Music library but I’m well north of 100k tracks. I actually sort and organize my music and its metadata with Swinsian.