I too had experienced Tyros vocalizer 'harmony' problems (occasional harmony mistracking (off key) and/or go in & out) . Luckily, I've now since found the SOLUTION to the problem, of which involed making a simple 'mic setting' change adjustment.

Previously, I had my

Mic Settings > Vocal Range, set to: "NORMAL". I've since changed this to: "LOWER" and now my keyboard's vocal harmonies track correctly and sound pretty clean and clear. The "NORMAL" setting is a 'compromise setting' to accomodate BOTH male & female voices, but the "LOWER" setting is more specifically targeted for optimizing VH to a lower (baritone/bass) voice like mine.

Though my TC Helicon "VoiceWorks" sounds perhaps better, I'm now very content with the Tyros Vocal Harmony results for live performance, and even find it acceptable (in some instances) for song recording as well.

Ed, before going out and spending extra $ on an external VH, please try my suggestion and let me know your results.

Good luck.

Scott