I received my YM2149 Synth from Catskull Electronics a few days ago! Thanks to David for the cool extras included 🙂
Having lots of fun with it! I've modified David's fork on Github to enable it to play back YM files over serial. It uses a C# app to parse the YM file and stream it over USB with the Teensy in Serial mode.
Cool thing is there are lots of cool songs in YM format that you can play. My musician friend SpaceFractal uses Vortex Tracker to make tunes and it can export to YM format for playback on the YM2149 Synth!
UPDATE: You can download YMPlayer from here