Hi Keyboard Master,
Please note that after making changes in the YEM to a specific voice, you will need to re-install this pack (along with any other packs you also want on the S770) on the S770. Otherwise, the changes made are only in the YEM, but not on the keyboard.
By the way, I also recommend re-exporting the changed pack in .ppf format from the YEM. This is the only way you will have the changed pack available again later (e.g. in the event of a possible problem with the YEM).
P.S.
You could possibly also solve the problem mentioned (some notes with too low a velocity on a certain Style channel) by editing the relevant style on the S770 in the Style Creator with the Compression function (Style Creator > tab Groove > Dynamics > Expand/CMP). Please see page 39 in the S770 Reference Manual.
You could also edit the Style as desired in the MixMaster PC program.
Best regards,
Chris