Wiz6 and Wiz7 try to abuse the OPL to use it as a crude DAC if you configure them to use SB or Adlib for sound. Other games such as Metal Mutant do this as well.
DOSBox does not support this! 🙁
You have to use PC Speaker for the sound setting to get decent digitized sounds in DOSBox with the aforementioned games. Note that for some reason the PC speaker sounds do click/pop in DOSBox at the start and end of each sound played.
Also, as a side note: I have two versions of Wiz6, one on original floppies that has no mouse or sound blaster support and one from the Ultimate Wizardry Archive CD-ROM that has mouse support and a fancy title screen with a party of adventurers pictured and scrolling credits. I still prefer playing with mouse support disabled because it feels more efficient 😀
My impression from multiple indications was that they intended the original release to have mouse support but didn't get it working in time.