If you happen to own two synths of the same model, you need to add the same device driver several times. A number then gets appended to the name (Korg M1 1, Korg M1 2 etc.). You can later rename each device, see below.
P A warning for when you later change your Setup in the middle of a session: If you add a Device, all Data Dumps for all devices (see page 167) that you have in computer memory, will be erased. If you wish to keep them, save to disk before you open the Setup window and add device drivers!