Damion,
I'm sure you know this but in order to connect a Motif ES with Cubase 5 you'll need a computer... it is the single most important item in the connection... not only the Type of computer but the Operating System. Cubase series 5 dates back almost a decade, so first thing to check is whether or not the software can be run on your current computer.

Although Cubase 5 is about a decade old and the Motif ES is that old and more, it is highly unlikely your computer is that old. In which case, you'll definitely need to verify if your current computer can even run that old software.

It is the software and the computer hardware that get fatally out of step... your MOTIF ES will be able to act as your instrument. You will need to verify that your current computer can run your hardware.

When your software gets to be four generations out of step, you may find the word non-Compliant showing up- meaning some functions are no longer going to run properly. You can verify where you are through your My Steinberg Account, they will be able to tell you exactly what software you should upgrade to to run on your computer for best results.

Once you get a software/computer match we can help you get up and running.