There is a difference between the printed and online manual.
printed manual says to use "import to db" functionality (there is none on the unit) but online says "scan music db" to add files or folders to music db.
When you use the "scan" option files will indeed move to the music db but only as long as the USB is in place. The usb has the file and the music db has an index.
The copy function appears to copy, but will not allow you to place the files in "my music" which is in the Browser>HDD1. Also, you cannot write directly to the music db.
The manual also says "※ NOTE: If you copy files or folders to the ‘My Music’ folder, those copied files or folders will be scanned automatically then
added to the Music DB"...........As i said, it will not allow it.