Never heard of Beyond Twilight, but I don't find Kamelot and Adagio to be particularly dark. Nevertheless, you might enjoy Pagan's Mind. (Start with Celestial Entrance.)
Check out Serenity, they're one of the best up-and-coming bands who play music much like what you're looking for...
Here's stuff on their first album:
Here's stuff on their second album:
They've toured with Kamelot and Threshold before and they're getting ready for a tour with Delain next year in support of the new album they're finishing up right now.