From Anti Martikainen, you have the Novum album which is one of the few specifically sci-fi. Many of the others are more med-fan. But in a feudal universe, you can still use many of the musics.Antti Martikainen - The Last Chronicle, Enter Infinity, Synthesia, Origins, or, indeed, just about any of his albums. (Yes, these are all full-length albums, some of them extended length albums, Those four alone are somewhat more that five hours of very epic music.)
Holst's Planets symphony - oh, come on! This one was a gimme!
Erich Kunzel's Time Warp - if you're sure you can keep your players from trying to lynch you.
Dragonforce. Pretty much their entire discography.
Or, if you want to really throw your players off their stride, the Hu or Wardruna.
I can add Two Steps From Hell. A bit different from Epic Score (more for a medieval ambiance) but quite good & epic...
I also found Miracle of Sound with a very broad kind of songs, generally inspired from computer games and movies/series. You'll have a lot of different ones, from Cyberpunk themed, Assassin's Creed (all era), to Irish/Celtic.
The HU have one song made for a Star Wars game (Jedi : Fallen Order). They can easily be used for a more unusual or 'alien' ambiance.