Pyotr Meshchaninov was an important organizer of chamber concerts using members of the State Symphony Orchestra. Unfortunately nine out of ten applications were turned down. Programs featuring composers like Gubaidulina and Denisov were typically rejected with the Party representative simply crossing out their names!
Very occasionally Gubaidulina received a performance abroad. In 1971 the Royan festival in France featured Eastern European composers and two works by Gubaidulina were performed, the Piano Sonata and the premiere of Concordanza, a new work for chamber ensemble. I suspect that this piece may be been revised at some later point as one writer, Doris Redepenning, refers to four instrumentalists, but the performances on YouTube have ten players. Here is the Esbjerg Ensemble:
One thing that stands out are the enormous contrasts: between simple unisons and massive dissonances, between soft, slow harmonics and rapid cascades of percussion, between fierce rhythms and lyrical melodic passages, between clearly defined pitches and glissandi. But at the same time, one has the sense that everything is there for a purpose. What I enjoy about this performance is how they handle it as chamber music, without a conductor. You can see the musicians providing one another with cues, which leads to a more unified performance.