Don ... another nice job ...
I also use a digitech which I think is great:
http://www.zzounds.com/item--DGTVOCWORKwhich unfortunately is no longer available ... it has a great feature in that there are a number of harmony presets that just follow your singing voice with no MIDI connection needed ...
Since owning the Pa900, I've discontinued using the digitech for one hour NH/Assisted Living gigs because the on-board VH is more than adequate ...
This summer has been VERY busy (fun busy mostly - traveling, visiting family and friends, having family and friends up to RI for visits), but once it slows down I want to do some recording and compare the two harmonizers ...