Lots of folks really like the 'extra' tones and rhythms. Most of them seem like variations of the internal tones (IMO)...but on the other user site http://www.originalz.com/casio/casio_bbs/
many of the users have made their own samples. The Casio free software is a great tool to build your own rhythms/tones. You can make a style from your favorite midi files (It takes a lot of work...but can be done...with good results).