For everyone thinking it's not worth the time, I've made a video with multi audio. You can get it here :
http://ovh.kabalo.org/media/full_intro.mkv EDIT : Link is broken atm. I will look into it when I remember (12/2018)
The default audio is the default GOG install. I advise to open it with VLC, as it will show you what is each track. In order, it is :
1) Default install
2) MIDI with Microsoft GS
3) MIDI with TimGM6mb
4) MIDI with ChoriumRevA
5) MIDI with Timbres of heaven 3.0
6) Roland with Munt and CM32 roms
Audio is not synced, some tracks worse than others. Note that ToH is much louder than other tracks. Be carefull when you switch to it.
Personnally, I don't like Roland, it sounds muffled and electronic. I prefer Chorium or ToH.
And imo, X-Wing default is not that bad. I tried with adventure games, S&M, indie, simon, and GM blows out the default. It is also awesome in Duke Nukem. This post should be cleaned up a little and posted on the general forum.
Or we could make a thorough tutorial on gogwiki or pcgamingwiki.