looks like a driver problem.
also with wdm drivers you should be able to come as close as 5 - 10 milliseconds.

I don't have cubase or the yamaha card, but I think cubase wants the asio drivers and looking at the name of your card, the yamaha want's the wdm drivers.
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Keyboards/Sound Units: Kurzweil 2600S, Roland VR-760, Acces Virus C, Roland G-800, Akai AX60, Minimoog, Machine Drum, Roland R8-M, mediastation x-76