The Chicago Chamber Musicians are a curious bunch. Staffed mostly with CSO first-chairs, this chamber collective of seven core members ought to have established a strong presence in the city by now. One reason it hasn't, I think, is its generic repertoire: sure, it's nice to hear Larry Combs playing his clarinet and Gail Williams tooting her horn, but does it always have to be Mozart and Brahms? The group's latest concert program is a case in point. Both Schoenberg's string sextet Transfigured Night and Copland's ballet suite Appalachian Spring are indisputable modern masterpieces that deserve to be revived--but they have been in the Chicago area just in the last couple of seasons. Only the third work, the 1956 Trio for Horn, Violin, and Piano by the Francophilic British composer Lennox Berkeley, is relatively unfamiliar. Among the other prominent instrumentalists featured are pianist Deborah Sobol, violinist Joseph Genualdi, flutist Mary Stolper, cellist John Sharp, and violist Richard Young. Sunday, 7:30 PM, Pick-Staiger Concert Hall, Northwestern University, 1977 South Campus Dr., Evanston; 342-5226 or 708-491-5441. Monday, 7:30 PM, concert hall, DePaul University, 800 W. Belden; 342-5226.