I saw a fair few posts looking for this solution so here it is...

Edit the file SINGLE.BAT and add "MIXER CDAUDIO 0:0" above the line "KEEPER.EXE"

All the music is played from the CD, or ogg files in this case, so the music slider has no effect. This will turn off CD Audio before DOSBOX loads Dungeon Keeper. Same for the other games and the BAT files are all in the same directory.

For those who haven't done much exploring of Applications on a Mac may not be easy to find. The default location of these files is below and you will need to use "show package contents", if you go via finder, on Dungeon Keeper Gold.app in both Applications and the sub game directory.

/Applications/Dungeon\ Keeper\ Gold.app/Contents/Resources/game/Dungeon\ Keeper\ Gold.app/Contents/Resources/Dungeon\ Keeper.boxer/C.harddisk

Hope this helps others trying to play this classic.