Sound Quality
Basic stereo was clean, with little audible hiss, even at ear-piercing volume levels. All Windows audio functions, including playback of multiple simultaneous sounds, were handled well. There just isn't much to talk about in this department.
General MIDI playback was outstanding, and XG MIDI playback was even better. It depends which soft synthesizer you install and use, but Yamaha isn't considered the MIDI leader for nothing. Though the sound is excellent, it's difficult for me to get excited about MIDI these days.
Historically, the big advantage of MIDI was to offload sound processing from the CPU and RAM to the sound card. Instrument samples were stored in ROM, and playback was handled by the sound card. You could compose a song using only a few hundred bytes of RAM that would sound fantastic and take virtually no CPU time… that is, assuming the user had a quality sound card. In reality, what the user ended up hearing could be quite different from what the developer intended, depending on what sound card they had.
The death of MIDI?
With that in mind, you can probably understand why game developers have largely ignored MIDI in favor of rebook audio spooled directly from the game CD. Redbook audio is guaranteed to sound great on any sound hardware. But this approach has its drawbacks, too, Music streamed from CD is static. It cannot change rapidly based on game events; in most cases it's the same music looped over and over.
Now that memory is so cheap and computer speeds are so fast, it's more cost effective to store MIDI instrument samples in system RAM and let the CPU handle most of the processing. In effect, you get dynamically downloaded instrument sounds, mixed in real time. This is the best of both worlds: the interactivity of MIDI with the guaranteed fidelity of CD audio. There is an emerging standard for this approach, called DLS, downloadable sample format, which the Waveforce currently supports.