Can I mention Ustvolskaya? Would that be considered "chamber music"?
Galina Ustvolskaya studied under Shostakovitz, and seems to have been Prokoviev's muse for a while. Very little is know of her, as she lives the life of a recluse in Petersburg, writing her music in that city's elaborate parks.
A quote from her
biography:
Ustvolskayas music sounds like nothing else. She is a very original composer and it is hard to describe her music in musical terms. The Dutch musicologist Elmer Schönberger calls her The woman with the hammer while the Russian composer Victor Suslin uses the term black hole, a galactic constellation of such an enormous density, absorbing all energy and light in it.
Many of her composition are extremely violent with dynamics up to fffff. But on the other hand she always gives instructions to perform her music espressivo, even with dynamics like this and even if the sound comes from banging a hammer on a wooden box (Composition No.2). The music is rhythmic and many times even ritualistic. One could even find traces of minimal music in her compositions. Some of composition have religious subtitles, but she never was a very religious woman in the usual sense of the word. For her, religion is living together with nature, respecting living creatures and even talking to birds and ants. Her decision to live in seclusion is reflected in her music, which also goes its own way.
I'm sorry if you were "getting to this", capnreverb, but Ustvolskaya is so singular, so "otherworldy" (in the truest sense of the word), and so special to me... I couldn't resist to mention her.