jamyskis: Those games that have Soundblaster or Adlib support are configured to use the best option available.
With some exceptions here and there, like for some odd reason GOG has chosen to default to Adlib/SB music in Strike Commander, even though there is also General MIDI support available for it (Soundblaster still plays the digitized sounds and speech on the side, though).
(IMHO the best music option for Strike Commander is Roland MT-32 though, but then you need a real MT-32/CM-32, or use an emulator like Munt. For most General MIDI is probably good enough in Strike Commander, but the Adlib/Soundblaster music is just awful).
I think they had the same also for e.g. Little Big Adventure. For some other games, GOG has chosen the best option, like General MIDI + SB for Privateer.