The fastest way, if you are wanting to move a lot of music, is to connect the tablet to a computer via USB cord. Move the music from the tablet to a folder on the computer, then change from access to the tablet to access to the SD card (while still connected via USB cord) and then copy the music over to the card from the computer.
NOTE: I say copy back as to leave a copy of the music on the computer. That way, should you somehow lose the phone or the files, you have them still on a computer. It is always good to back up all personal stuff regularly.