It is installed with "Korg M50 External Setups" (M50_ExtSetup_e.exe), which is on the CD that came with your M50. After installation you can find it in: C:\Program Files\KORG\M50\M50 External Setups\Steinberg\Cubase or, if you have a 64-bit system, in: C:\Program Files (x86)\KORG\M50\M50 External ...