I don't know why the X-series need to be updated, i am still very happy with mine as it is.
The Ketron's are build around the SAM9407 (newer version SAM 9707) sound-chip.
Please see this link http://www.atmel.com/dyn/general/tech
especially chapter 2.5.2 for more information around SND-format sounds. (just a tip)
Greetings from Belgium !