Cynthia uses whatever midi playback device you have on offer. By default that's "Microsoft GS Wavetable Synth" on Windows, which is horrible to say the least. But if you install a 3rd party midi driver app like VirtualMIDISynth or OmniMIDI (see my other comment in this thread about soundfonts) you can upgrade sound playback to high quality using soundfonts (.sf2).
The app can also switch between up to 10 midi devices in realtime, or use them all simultaneously for playback - see main GUI, bottom right, Playback Device, 1 to 10 or "A" for all.
App supports General Midi 1 (GM1) over 16 channels in playback formats 0 and 1, but not 2. It does not support General Midi 2 (GM2) e.g. 32 channels, and does not support "system exclusive messages".