Well… difficult to be answered.
First question might be: HOW authentic music should be taken in KC: D?
Next question: What effort should be taken into music?
Etc.
For an unknown reason, I would be pretty curious about the 'Horses to make it pretty much authentic to the point, that you’ll hear music only in cities/castles and maybe taverns. And otherwise none. But instead, to arrange the environments noises as some kind of music. The swaying of the corn (if not harvested yet) in the wind the tchirping of birds and noises of the woods…Behind the player a snake hushes over the ground… And then the sounds of the next settlement growing, when getting nearer…
For “real” music, it would be kind of nice to get some recognition to “modern” times’ view of medieval music. In Germany we have some quite interesting (and more or less known) music bands making medieval folk music. (“Faun” and “Schandmaul” might be the most famous with their older set of songs, although the latter I won’t sort to “folk”-section…But “Die Irrlichter” as a less famous, but nonetheless more authentic(al?) music band with some fantasy-themed songs as well, also “Die Streuner”, “Versengold”, erm… I could mention some more…
But I guess you’ll have some examples of your own… )
Oh, I almost forgot: For ‘The Elder Scrolls Online’, they made some beautifully chanted songs (at least in my language’s version it sounds quite good :D)
Edit:
Well, Skyrim had an awesome “main theme”, I do think, although it wasn’t much orchestral as such. Some choral things would be quite fine, supported by minimal instrumentalization. Also on behalf of religious issues due to the time KC: D is placed.
Orchestral… I don’t know about that. Instruments as violins, celli and such aren’t quite old yet. My girlfriend and I bought a Rebec a few days ago, which is said to be the predecessor of most string bowed instruments of today (with some stoppovers at baroque, and renaissance etc. as well, of course).
(https://www.youtube.com/watch?v=zNvPJ2Fuzns)
(Reason for second editioon: Correcting some typos, add little sense to argumentations (choral vs.orchestral))