One thing to watch out for (and probably a good reason Yamaha haven't updated their harmonizer for a long while) is that Yamaha Corp. don't make a standalone harmonizer...

They don't have a pro product in the field to drive along technology and allow some trickle down to the arranger division. Korg license TC Helicon technology, one of the industry leaders in pitch shift technology, Roland have their own pitch shift technology used in the VP series, but Yamaha don't really have anything standalone like that.

They ought to have a try to license Eventide stuff... some of the best vocal pitch shifting I've heard. Or, even better, license the Auto-Tune algorithms, nowadays, the industry standard for pitch correction (which, to be honest, many of us need a lot more than fake harmonies!) and some good auto harmony software.

OTOH, you could just play with good singers...