I would also recomend Michael Tippett´s String Quartets, Stravinsky´s Concerto in D, Three Pieces and Apollon Musagéte (the Stravinsky pieces are for string orchestra)
He will be missed, a wonderfull conductor, I had the honor to play under his batton once. (Sixten Ehrling was also pricipal conductor for Detriot symphony orchestra 1963-1973 and professor ar Juliard 1973-1988) 8O