Oh my, haven't heard canyon.mid for years - takes me right back. Have you tried either of the soundfonts below? They do a pretty good job a reproducing canyon.mid, not perfect, but enough to take you back. The default Windows "Microsoft GS Wavetable Synth" is rather horrible at sound reproduction at best, and that's being nice.

a) 3 Mb OPL3.zip (contains one file "OPL3.SF2") - compact but pretty good: https://www.vogons.org/download/file.php?id=45715

and was sourced from: https://www.vogons.org/viewtopic.php?t=59354

b) 128 MB OPL-3_FM_128M.zip (contains one file "OPL-3_FM_128M.sf2") - a bit larger but slightly better in my opinion: https://musical-artifacts.com/artifacts/15/OPL-3_FM_128M.zip

and was sourced from: https://midis.fandom.com/wiki/OPL-3_FM_128M.sf2_(OPL3_Yamaha...

You can direct Cynthia to output her midi notes/instructions to a different midi device/devices for higher quality playback/sound reproduction through the midi driver apps below (for Windows):

a) VirtualMIDISynth (supports up to 4 simultaneous drivers with option to use one or more different soundfonts per driver): https://coolsoft.altervista.org/en/virtualmidisynth

b) OmniMIDI: https://www.majorgeeks.com/files/details/keppys_synthesizer....

The apps above do a nice job at playback with minimal lag and without much setup or tweaking to get going. Basically just install one, assign a soundfont, and restart Cynthia to be able to select a different midi device - numbered 1 to 10 under Playback Device (bottom right panel of main GUI).

At one point in the past I did look into including soundfont support directly into Cynthia, but instead decided to focus on playback stability and ease-of-use as top priorities, which funnily enough was a mountain enough all-by-itself to climb considering how difficult Windows can be to get along with, let alone get working right on something as simple as midi playback under Win32.