Definitely the new-music event of the fall season, Ensemble InterContemporain's return marks the group's first appearance here in seven years. The well-known collective of 31 soloists--founded in 1975 at the request of the French Ministry of Culture, led by Pierre Boulez, and affiliated with his Institut de Recherche et de Coordination Acoustique-Musique, the Parisian citadel of music research--has become the most potent force in the European avant-garde, having premiered more than 300 compositions, at least 100 of them commissions. Broad-minded and avowedly internationalist, it has a repertoire of 20th-century works that encompasses the entire spectrum of modern aesthetics. Which makes one wonder why so much of the program for this concert at Pick-Staiger is devoted to the old guard. It's always a thrill to have the most interesting and challenging contemporary works illuminated by Ensemble InterContemporain's exemplary performances: the mind games of Boulez's Derive I and 11, the final version of Gyorgy Ligeti's Piano Concerto (1987) in its local premiere. But how about a contribution or two from the younger generation? As it is, only Les eaux etroites by the French academic Antoine Bonnet qualifies as such. The ensemble will be conducted by Boulez, arguably the most empathetic interpreter of new music; Dimitri Vassilakis is the soloist in the Ligeti. Sunday, 7.30 PM, Pick-Staiger Concert Hall, Northwestern University, 1977 South Campus Dr., Evanston; 902-1500 or 708-491-5441.