The most devastating blow to the Fast Track C400 came with macOS Catalina (10.15). Apple completely dropped support for 32-bit applications and kernel extensions (kexts). The original M-Audio drivers for the C400 were built on a 32-bit kernel extension architecture. Once you upgrade to Catalina or newer, the operating system literally cannot load the driver.
If you are using macOS 12 Monterey, 13 Ventura, 14 Sonoma, or 15 Sequoia, you are in a difficult position. M-Audio has moved on to the M-Track series. m-audio fast track c400 driver mac
Earlier versions like 1.2.11 and 1.0.4 supported older systems such as macOS Sierra, El Capitan, and Mavericks. The most devastating blow to the Fast Track