I'd load the floppies onto a PC, organise into a set of subdirectories and then use a thumbdrive or a card reader.

If you don't want to take the card out of the keyboard, you can use Yamaha's "MusicSoft Downloader" to transfer files to/from the card via USB but it isn't fast and the operation of the software package is functional rather than enjoyable.

If you have a digital camera that uses SmartMedia you may find you can use this like a card reader. In "transfer" mode on my Olympus, the smartmedia card appears as a removable hard disc device when I plug the USB cable into the PC.