Hi Anthony,
The Vocaliser/Harmoniser is built in to the KN7000 and also the KN6xxx. It is a voice processor which can add harmony to the mic input. Generally, the harmony is determind by the chord currently being played by the left hand, on a split keyboard, but there are other options. There is not a dedicated 'Harmoniser' button on the keyboard - it is accessed via menu items (on KN7000 Program Menu/Reverb & Effect/Mic Reverb & Effect) and can be controlled by a footswitch.
I'm not sure if the PR804 has this facility but if it has, you should find some reference to it in the User Manual.
Much has be written about the Harmoniser in this forum and the general opinion seems to be that it is a waste of space
If you want a good vocal harmoniser the one which the 'Pros' use is the Digitech.
------------------
Willum