Bome MIDI Translator Classic (free) or Pro (paid) is the definitive solution for legacy MIDI controllers. It acts as a virtual driver, listening for the Radium’s proprietary messages and translating them into standard MIDI CC that any modern Mac app understands.

You can likely use the original M-Audio USB MIDI Driver v3.5.3.

Before you frantically search for a downloadable file, you must understand a fundamental shift in how macOS handles audio devices.

The M-Audio Radium 49 is a "Class Compliant" device for basic MIDI notes, but to use the advanced features (assignable knobs, faders, and the "Advanced" button functions), it historically required a specific driver from M-Audio.