I used my Digitech Vocalist 4 set to key to do this. In the music IQ setting the machine reads your voice so no chords are involved.
I think Digitech makes great harmony and would love to see Yamaha link with them the way Korg has linked with TC Helicon.
The way you describe setting up harmony could work for the studio, but I'll take my Digitech for live performance. I have this EAGLETS 3 style set up in all the keys I like to sing in so it's just a matter of stepping through to the right key and starting the song. Of course I use other settings like 3UP and ALT GOSPEL HARMONY. They all produce great results for my music.
Give this a listen and let me know how you critique the harmonies.