That is so true YM. As he comes down that huge staircase it almost seems like some kind of dance. And even his movements throughout the entire beginning sequence seem to flow with the strains of the melody.
I know that the piece that Jennifer Wells is playing when she is hit over the head is Chopin's Etude #13. But I believe she is playing a different piece when John Cassavetes first enters the room.
If it's what I think it is, it's part of the same piece that he plays when he's approaching Williamson Ranch in the fake nighttime car scene: Brahms Piano Concerto Number 2 in Bb.
Love those early TV night scenes - put a dark filter on the camera, shoot in sunshine (so it looks like moonshine), turn on the headlights and play chirping cricket sounds LOL