You don't need a style converter disk to play the kn5k style disks. Just load the style and save it back to disk in kn6k format. To use earlier than the kn3k styles you will have to have access to the next step-up keyboards and do a load and save until you reach the kn3000/5000 level. Very time consuming, but better than losing the styles.
If people want to use the on-board styles, thats fine. Me, I like variety and will only use a style one time for a recording, and never again.I convert a lot and though time consuming in some cases, it saves starting from scratch. I started a library with notes when I first started conversions and it saves me a lot of time when I'm trying to find a style to fit a certain song. I may go through 30-40 styles to find the one I need, so a few thousand isn't too many. If a performer plays the same tunes over and over, then only that many styles would be needed, and the on-board styles may do the job. Hey, whatever it takes to keep the music alive!