Clif, Akai DecaBuddy seems to do an excellent job. You can create nice rich harmonies using either midi notes or fixed harmonies. There is no noticable latency when using it in forte Ensemble (or even in Cubase SX - Amazing).
It has been a long time since I first started using DecaBuddy but if my memory serves me right there were some glitches in the demo and the purchased versions. I phoned Akai and they made an updated version available (v1.01) and everything has worked well ever since. If you go this route make sure you get the updated version and if necessary contact me.
[This message has been edited by Frank L. Rosenthal (edited 10-15-2003).]