Plug the USB into your Mac. Open Applications > Utilities > Audio MIDI Setup .
When the Radium 49 was released (primarily during the Mac OS X Tiger and Leopard era), MIDI class compliance was not as standardized as it is today. The Radium 49 was designed to interface with computers via USB or standard 5-pin MIDI cables. m-audio radium 49 driver mac
So, what do you do?