Well, David, how nice to find someone out there has the same taste in music that I do. Shostakovich's Preludes and Fugues, when played by Shostakovich himself, is the most beautiful piano music I know.
I never did really like Elliot Carter's music (too academic) and I do not know Ferneyhough at all.
For the first time in a long while I played Bill Hopkins (wonderful!) and now the Barraque sonata is on. Discovering Stockhausen's piano music a few years ago was a delightful surprise. I was ready for the axing of the pianos and it is anything but that.
Best of all is Morton Feldman's piano music. He was a close friend of and was heavily influenced by the abstract expressionist painters.
And there are so many others.
Ed: Bartok wrote six well-known string quartets, #1-#6. At first it takes repeated listening to get it, but after a while the music is as easy to listen to as the music of Mozart. If you are not used to it, you may have to perservere.