Great finding of such a beautiful retro site.
Basically you want to inflate all "naked" Mac files on a Mac (emulator) with StuffitExpander.
The apps are useless otherwise as the Mac resource forks are lost.
To get going for now, feel free to try this:
https://www.magentacloud.de/lnk/2cYMpbWP
The files are re-packaged in a zipped .img container.
Unzip and add the .img to your SheepShaver volumes tab.
This version of Music Mouse is 68k coded, so it should work with Basilisk II and MiniVMac just the same.
Maybe you could ask the author nicely about an unlock code?
Kagi is down for some years meanwhile, as you will know.
Edit 1:
Neither SheepShaver nor Basilisk II do work with Music Mouse on my side.
What does work, however is MiniVMac II.
Moving the Mouse in the app Window does play some tunes.
Note that Output has be set to Quicktime - default is MIDI.
The app window has to look like this to generate sound:
Edit 2:
Seems like MiniVMac ii is the only way to play MusicMouse for me.
That would make sense, as the Mac II was among the first Macs to support Quicktime.
Anyway, MiniVMac emulating the Mac Plus can not play MusicMouse as QuickTime can not be used on it.