MIDI Preview in MediaBay

I have recently moved from Windows 8 to Mac. I cannot preview any MIDI loops (.mid files) in MediaBay. On Windows 8 this used the in-built Windows Wavetable Synth, but there isn’t a default equivalent on the Mac.

How do I do an equivalent of this on a MAC? On my set up, the ‘MIDI Output’ drop-down in the Scope section of MediaBay only shows the options ‘Not Connected’ and ‘Oxygen 49’ (my USB Keyboard). I obviously need to define or install some sort of device to play the previews but I don’t know how to do this?