You can start there or haven't your synth have MIDI?
Mac OS 9 Lives! (Classic Mac OS Forum) » Classic Mac Hardware (Troubleshooting, Upgrading, & Modifying) » DAW - Digital Audio Workstation (Audio Interfaces & MIDI Hardware)
or maybe somebody (administrator/moderator) should make here new place, because analog synths not fits very well there, although it might have MIDI. Something like:
Mac OS 9 Lives! (Classic Mac OS Forum) » Classic Mac Hardware (Troubleshooting, Upgrading, & Modifying) » MIDI - Synth & Drum Machine