i have used the PLG100VH board (the same harmoniser thats in the Tyros/PSR series) in my s90es, i have used the TC-Helicon one on the pa1x pro, and the harmonizer on the sd1+...far and away (and i mean daylight second!) is the TC-Helicon unit found in the PA series, the only one that remotely comes close is the ketron harmonizer.i use the harmoniser both playing live chords and pre-programmed(by me) harmony tracks in midi files..no question TC Helicon wins everytime...( i demoed the new digitech vocalist II a while ago, and its useable but not in the same league either) sorry to rain on the yamaha/and others parade, its just my opinion on the available harmonisers i have actually used/tried.
cheers
PS just wanted to add FWIW!!

[This message has been edited by miden (edited 09-27-2007).]