Hi James,
Have a read over the reference manual section Setup > Setup Your Midi Devices which will walk you through the process of setting up keyboards with Studio One step by step.
As relates to the Motif Editor Software, that's a bit of an unknown. That is to say, even though it's a plugin and it should load into Studio One like any other plugin, we don't know how it chooses to address that keyboard or if Studio One's external device midi ports will be exposed to it for talking to the keyboard when it's running as a plugin. The thing to do in that regard is to load it and see what the configuration screen presents to you, look see if it has access to the Studio One external device midi ports that you setup in paragraph above.
