Curious; I don't think it has been updated for a long while, but have you tried to get a hold of the 32bit .dll and convert it with jBridge to a 64bit version?

BTW i tried all sorts of audio harmonizers for vocals mainly. IMO there is one which can work, quite expensive though. Hardware unit from TC electronics, VoiceLive Rack, which i have used with acceptable results in a studio situation. There's an Eventide hardware unit also that was quite popular years ago in luxury studios, i never got acquainted with it. I think it was commonly used rather for thickening vocals etc. But i never heard a software VST version that provided natural sounding harmony vocals sofar .... F