Squeak.. here is the link to the WK3500.
http://world.casio.com/me-africa/emi/high_grade/wk3500.html The site says 10000 notes. Only six tracks per song too.
I agree luk, although it wasn't so much that the drums that sounded that bad to me, but moreso that the internal patterns themselves were not so good. That's really what killed the MZ for me, along with zero aftermarket support from Casio.
The wk3500 apparently uses the same sound engine as the MZ did ( ZPI I think is what they call it ), and there were some very good sounds mixed in with some that I didn't like very much at all. At the time I liked some of the sounds ( but certainly not all ) better than their counterparts on the PSR740. Particularly good on the MZ were the electric guitars and the sax patches, along with some excellent synth sounds. I wonder how much editing is available ( I do see it has user sounds ). The MZ had a very detailed but simple to use and understand synth editing engine; perhaps the most intuituive one I've ever used on anything.
I'm actually mildly interested in trying this one out. One reason is that I would like a 76 key controller for the Motif ES, and while it didn't have the feel of a weighted controller, the MZ had a much better feeling key touch ( for me ) than any of the non weighted Yamaha's I've used. If it could actually be useful for the occasional sound or two, and maybe one or two other things, then I might consider it. The Roland A37 controller costs roughly about the same as a WK3500... so perhaps a tryout is in order.
AJ