an sd card can be backed up by simply dragging the contents of the root to a folder via a card reader (and then dragging back to a different card). Zip it up if you want a single archive file.

Audio will not be backed up, but then Audio is not backed up via Song Manager or via SD Explorer (where it is inappropriately zipped up in a waste of storage space). For audio you have to use the Jukebox program, but for Technics and Midi there is no problem with drag and drop.