Preliminary support for MSU-1 audio has been added to the unstable nighly builds of the SNES core and MiSTer Main. If you want to give it a try you will need to download both of these (SNES and Main) from the unstable nightly GitHub branch.
Credit for the MSU-1 audio support goes to Karl Lurman/dent^nz , ElectronAsh and Sorgelig.
Once newer updates have been committed they will be shown after the file name given in the below download direct links, you can check these repositories for the latest links to see if an update has been made:
Latest MiSTer main unstable nightly releases here:
https://github.com/MiSTer-unstable-nigh ... /releases/
Latest SNES core unstable nightly releases here:
https://github.com/MiSTer-unstable-nigh ... /releases/
Download unstable MiSTer main (MiSTer_unstable_20220515_14d7f7) as of 16/05/2022 here:
https://github.com/MiSTer-unstable-nigh ... 515_14d7f7
Download unstable SNES core (SNES_unstable_20220515_13f0e8.rbf) as of 16/05/2022 here:
https://github.com/MiSTer-unstable-nigh ... 13f0e8.rbf