If what you're looking for in music is 'darkness', why don't you listen to metal/hardcore/electronic? Classical music is, in general, too multidimensional to fill adequatly these kind of cravings. Where modern music succeeds in my mind, it's in its ability to pinpoint those very specific emotions, ambiences, etc. and to convey them into music in a simple, but highly efficient manner, while the classical composers seemed to prefer a more all-encompassing view of things.
I mean, I haven't heard all the music that's been composed in the entire history of mankind, but I can tell you that so far, I haven't heard anything (in classical music or otherwise) that sounds darker than Incantation, angrier than Minor Threat, more assertive than Amebix etc.