OK, found the solution here: https://forum.dune2k.com/topic/21510-problem-solution-dune-in-dosbox-without-sound-what-to-do/
1. in your profile’s Software settings, select duneprg.exe as Main program
2. click the small cogwheel icon, and paste the following line: ENG VGA SDB2207 EMS 386
3. make sure you’ve set the sound config to Soundblaster for music & sound (or configure it accordingly)
4. run the game
That’s my test profile: http://www.mediafire.com/file/55jfkowa6dkpiml/Dune.mgc/file
Just adjust the path settings, and you should be good to go.