You can find the fixed version here: https://www.gog.com/forum/star_wars_xwing_and_tie_fighter_series/new_winmmdll_fix_remastered_edition_on_windows_10
But alas it changes nothing and the game stubbornly refuses to run.
However, as suggested above I could not find the following dll in the game's folder:
Edit: Ok I just figured out the "3DFxSpl2.dll" and 3DfxSpl3.dll are in the Nglide folder, but even if I delete those two files
the game still refuse ton run :(
Just to be sure, you did remember to rename winmm.dll to win32.dll replacing the one in the folder right?
nGlide is a wrapper to allow you to run old Glide games on openGL cards as far as I can tell. Installing the newest version of nGlide will fix issues (like it crashing when you try to exit), but the older version which should be preinstalled with the gog release (and thus you needing to remove the files from the game folder for it to try using the new ones installed with the nGlide installer) should not impact the game actually launching.
As a test of this, I just uninstalled Pandemonium, made sure the folder was gone. Re-downloaded and reinstalled it.
Launched Pandy3.exe (where the shortcut points to): nothing happened apart from process using 100% of a CPU core until killed with task manager
Downloaded the winmm fix from the thread you linked to (Thank you very much). Unzipped everything (including the libogg and libvorbis files) to the Pandemonium folder. Renamed win32.dll to win32.dll.bak and renamed winmm.dll to win32.dll
Launched Pandy3.exe: Game launches with no issue, but not too happy with getting shut down as I didn't do any of the mucking about with nGlide.
And as a bonus, opened the properties of Pandy3.exe and removed the run as admin checkbox, game runs fine without being admin.
Edit: Thanks to SFriedt for mentioning you needed to rename winmm.dll, though the renaming it to win.dll does not work for pandemonium, the readme in the archive also mentions winmm -> win32