Update:
A "new & improved" Casio CTK-6000 WK-6500 INS file has been added to the link above. It now includes the new Instrument Name + Instrument Number for each tone. This makes it far easier to find them when using Cakewalk's Patch Browser.
BONUS FILE:
I also added in one for the CTK-7000 and WK-7500 keyboards. (Someone with those actual keyboards will have to test them to see if any other Controller Names need to be added to the file, but I doubt that's necessary.)
That's 10 Casio keyboards now fully supported with Instrument Definition files.
p.s. A CTK-6000, WK-6500, CTK-7000, or WK-7500 keyboard will be gladly accepted as a donation for all my effort. Here I am, tirelessly making INS files for keyboards better than mine, seems only fair.