The answer is the New York City Ballet Orchestra, playing live with the choreography of George Balanchine. In fact, one could say that Balanchine remains the major advocate for twentieth century orchestral music in New York.
I heard and saw an amazing program at the New York City Ballet as part of their "Black and White" series; which means just music and movement; no sets and simple leotard costumes. The highlight for me was the piece "Episodes", choreographed, in order, to Webern's "Symphony", "Five Pieces" op. 10, "Concerto" op. 24, and his arrangement of the Bach "Ricercar". I was incredibly moved to see what Balanchine had done with this music which I love so much; the choreography was subtle, inventive, and always consistent with the spirit of Webern's music. It's impossible to describe. I feel very lucky to be on a planet where I can go with 2,000 other people on a Sunday afternoon and hear these pieces.
The other 3 pieces on the program were exciting as well. A piece which was new to me was "The Four Temperaments", choreographed to a Hindemith score of the same name for piano and strings. I had not heard the music before. (Hindemith wrote many interesting pieces, especially early in his career, but his reputation suffers badly from some of the more pedantic and academic pieces he wrote. Not to mention those of us who suffered through his "Elementary Training For Musicians") The music works in an incredibly intricate way with the choreography, the dialogues between the piano and the strings being contrasted with various formations of soloists and groups.
I also love the "Duo Concertante", where Balanchine consistently subverts or expectations by having the dancers stop dancing and go stand around the piano and listen to the music. And the "Symphony in Three Movements" is always exhilarating.
Balanchine is an extraordinary artist; he really deserves to be on the same 20th century pedestal with people like Stravinsky and Picasso.
For further information, the New York Times was as excited as I was..
New York Times Review
