I'm building a 3D music education application using Unity and MIDI. It's designed to teach rhythm guitar by example by using 3D hands to play a 3D guitar. Right now, I have CoolSoft Virtual Synth playing all my Windows sounds with a GM soundfont. And I've used programs like Polyphone to create soundfonts from sound samples I provide.
I'm interested in the sound samples and formats that software MIDI players can use. I'm using soundfonts now and I'm only vaguely aware of the DLS sample format (which may be extinct for all I know) but there may be others. And there may be giant, high-quality sound libraries that some or many MIDI sound formats can access. What are the pros doing to get their software playable sounds?
I'm providing a screenshot and a link to a prototype web version of the application below: