It won't be a great experience, but for MIDI, wouldn't Microsoft GS Wavetable Synth suffice? Doesn't that come with Windows 98? If it's trying to use the nonexistent Ad Lib support, you can probably tell it to use GS Wavetable Synth instead in the MIDI settings?

The problem would be games/software that moves to DOS mode and tries to use SB16 MIDI then