Unfortunately it still sounds awful. Listened to my MIDI-versions via Winamp 2.93, activated DirectMusic /MS Synthesizer Output-Support, added Reverb and now it sounds the way it used to on my good old AWE 32 soundcard.
Since the gog-provided ingame-BGM is a .wav-file, i was confident to just switch them with ones i recorded (diskrwiter-plugin from WinAmp) and made my own, better sounding .wav-files of each of the original MIDI-Files. Sadly that didnt work, the game (its emulator) seems to have big problems with .wav-files with better quality eg. 22khz sampling and above, stereo sound, 8/16-Bit...
Please, dear GoG-team, fix this jewel from sounding so awful!