Having grown up gaming on PC speaker I only knew the wavetable MIDI miracles from hearsay. Now any time I touch some DOSbox retro memory I'm nothing but disappointed becausr those MIDI tunes? They are just that, tinny voyages through the general MIDI instrument set where well made PC speaker programming can have awesome roughness.
You should be able to force pc speaker only if you go through the config.
Many MIDI things sound better on old hardware than they do via modern reproduction. FM chips were very different from wavetable, and there's quite a lot of variation besides. It's no wonder some music sounds goofy, now --it was written with a very different palette of sounds.