M-Audio has marked the Radium 49 as "Legacy" and "Discontinued." The final driver released for this unit was intended for much older OS versions (macOS High Sierra and earlier).
Users have reported some success using this legacy MIDI-USB driver on versions as late as OS X 10.10 (Yosemite) Original Universal Binary driver for OS X 10.3.9 and early Intel Macs. Where to Download: While M-Audio’s main Support Downloads page lists many products, the m-audio radium 49 driver mac