Use a dedicated interface like the iConnectivity Mio or Roland UM-ONE.
SysEx (System Exclusive) is a specific type of MIDI data. Unlike MIDI notes or CC (Continuous Controller) messages, SysEx is manufacturer-dependent. For the Korg X3, SysEx files typically come in .syx or .mid formats and contain: Individual sounds and patches. Combi Data: Layered performances of up to 8 programs. korg x3 sysex files
Most modern DAWs (Ableton, Logic) can send MIDI files containing SysEx, but dedicated librarians are more reliable. Use a dedicated interface like the iConnectivity Mio
To transfer SysEx files to your Korg X3, you cannot simply use a USB cable. You need a bridge between your computer and the vintage MIDI ports. korg x3 sysex files