Yeah, I was going to say Dave Weiser is the authority on Kurzweil stuff.
Kurzweil doesn't exactly support seamless switching between sounds and I don't think they claim to. It seems to work well enough with individual programs, but not in multis and not at all if you use the KB3 engine. AFAIK, only the Korg Kronos, Korg Nautilus, a couple of the Roland Fantoms, Yamaha Montage, and some Nords support that (and if you use the Fantom's organ engine, all bets are off).