Scott,
A quck view at the Casio specs on the site, (surprisingly this keyboard is not listed at the European site), show an "HL sound source", which is what early Casio Privias were using, and what my 13 year old Casio is using. Their specs are very similar. The current one is the "ZPI sound source" found on Casio Privia and WK 3000 and above.
But if it sounds good to your ears, I think you can't get wrong for that price, it costs less than a good keyboard case.