Im thinking only how to solve a problem that occured in my setup, Ive already got an external keyboard midi controller (CME UF5), and when Im on only one instance of renoise, it works great, no problems at all. But when I start another renoise instance, and error occurs "Failed to open MME Midi device <<USB 2.0-MIDI>>
Whether or not you can open multiple instances of a MIDI devices usually comes down to the quality of the hardware driver.
But even when you come across such problems, there are workarounds, such as using virtual MIDI cables (for windows I can recommend loopMidi).
I don’t think this affects the Ohm64 though. Never heard Hitori Tori or others who are running multiple Renoise instances complain that this was a thing.