Mark, I know nothing about Macs so the advice I can give you is minimal. On PC's, the main problem with MIDI sound is that you have to go into MIDI setup and choose your external device as an input device, then choose a playback device, usually your software synthesizer. Your MIDI options might be something you can set up in Logic, or they might have to be set up in the system sound settings. Look for commands with the word MIDI and open them to see what options are available. Other than that, I'm in the dark what to tell you.