How well does the VH2 generate correct harmonies from an entire mix? Most people using these I've seen plug a guitar into them, and it derives the harmony from the audio from the guitar. But that is basically ONLY chording. A full mix (whether from an mp3 or an arranger's audio out) contains the drums, percussion, non-pitched sounds, as well as basslines, chords and lead lines (often with many passing notes).

If you are planning on using the arranger's main outs as an audio trigger for the harmony, you need to find this out. And I'd be interested too!