Now that I look at a Gravis Ultrasound online, the card looks primitive compared to a Soundblaster 16.

Also, the game came out before the Soundblaster 16; that is one reason the Amiga version gets a listen.

GUS is a different beast that supports hardware mixing while the SB16 doesn't, giving it higher sound quality when taken advantage. Sadly, this wasn't a common thing with DOS games.

It was widely popular in the demoscene though.