I highly recommend the 'Digitech Vocalist Workstation EX' for use with the Technics KN5000. Technics APC (auto-play chord) harmonies can be sent to the Digitech unit via midi when you play the KN5000 keyboard. Both the vocal harmonies as well as the audio quality itself on the 'Vocalist Workstation EX' are superb. In fact, I run my vocals thru the Digitech Vocalizer mic inputs instead of the mic inputs on the KN5000 itself, because the audio quality is much better on the 'Digitech Vocalist Workstation EX' then in the 'Mic Entertainer' section of the KN5000.
The sound quality and features on the 'Digitech Vocalist Workstation EX' is 'FAR SUPERIOR' to the 'built-in' vocal harmonizer included in the Technics KN6000 keyboard.
If you are a fairly decent singer desiring quality backup harmonies, then the 'Digitech Vocalist Workstation' is highly recommended.