Hi Graham,
hi Stephen,
The DGX-670 has a Style Creator, but with scaled-down functions. Above all, the List Editor is missing, so you cannot edit MIDI events directly. If you have changed the settings of the Style parts (e.g. voices, volume, effects) in the Mixer, you should be able to save these as a new Style if desired (using the Save option in the Style Creator).
P.S.
For the sake of completeness: As mentioned elsewhere, you can use the existing OTS in Styles on the DGX-670 (in conjunction with the OTS LINK function), but you cannot change the OTS of the Styles, because the DGX-670 does not have OTS buttons (1 - 4). So you have to save your own keyboard voice settings in the Registration Memory.
Best regards,
Chris