Hi flailman,
As far as I know, the same harmony notes on both keyboard parts is not possible with the DGX-670.
However, if you call up the "Keyboard Harmony" display ("Voice Effect > Keyboard Harmony > Type"), you could got to "Detail" and set the Assign to "Multi" there. Here is the description of this setting (quote from page 9 in the DGX-670 Reference Manual):
Keyboard Harmony > Detail > Assign
This parameter is available for all types with the exception of Multi
Assign. This lets you determine the keyboard part via which the harmony/
echo notes will be sounded.
• Auto: Applies the effect to the part which is turned on. When the both
parts are on, the Main part is given priority over the Layer part.
• Multi: When both parts are on, the note played on the keyboard is
sounded by Main part and the harmonies (effect) are divided to the
Main and Layer parts. When only one part is on, the note played on the
keyboard and effect are sounded by that part.
• Main, Layer: Applies the effect to the selected part (Main or Layer).
Hope this helps!
Best regards,
Chris