Swinsian

Swinsian is a robust music player for mac. It can watch folders from your external drive, or internal drive. It has very advanced features, and unlike the native music app, it doesn't take several hours to load. I have 900000 plus tracks in my library, and because it's folder based- I logged right into my mac, and started playing it, no load time. Plus, if you want to add something, you can add it to one of the watched folders, and it scans it and puts it in the library.