I have used my Mac Midiman interface (which looks similar to that one) with my PowerBook Duo (7.5.3) to play MIDI files on my synthesizer. What you need is:
* A good synthesizer (such as Yamaha PSR that I used)
* OMS (Open Music System) Extension (here)
* A midi player (such as Arnold's MIDI player that I used)
With that setup, you can play any MIDI file on your mac and the music will play through your external synthesizer. Back in early 90's that was really cool! (And still is
)