Regardless of where your music comes from, it must satisfy the following requirements:
Be free of DRM.
Be one of these music formats: WAV, FLAC, MP3, AAC (and I read recently that ALAC is okay too)
Be organized with a folder and file structure where a folder named for the Artist, contains folders named for the Albums, which each contain the track files for their respective albums. These folders may be contained in a folder named "music."
music\Artis\Album\tracks
Then you can use one of the followinging methods for the file transfer: Import via USB (formatted as FAT32); Upload via WebUI; direct copy via NAS followed by Scan Disk.
If you require further clarification on any of that, just ask.