Try switching USB modes (Settings/System Settings/USB Mode) to MSC. Auto Detect should do that automatically but you never know. Have you ever connected the Fuze to a Windows Computer? Because if you did songs may have been transferred in MTP mode instead. MTP works with Windows Media Player, which is obviously not on your Mac.
Your computer only sees one USB mode at a time. So if files were transferred via MTP, the Mac won’t see them.
