As a rule the big outdoor classical series aren’t noted for their sense of adventure; usually constrained by crowded schedules and a shortage of rehearsal time, they tend to stick to perennial favorites. Happily, Grant Park’s concerts this weekend are a departure from the norm. The three composers on the program, none of whom is a household name, are represented by works that are either out of fashion or totally obscure. What’s more, the soloist, keyboardist David Schrader, is a Chicagoan, not one of those out of towners called in to make the show “important.” He’ll join the Grant Park Symphony in the Symphonie Concertante for Organ and Orchestra by Joseph Jongen–renowned in his native Belgium, but still mostly a pet cause of Schrader’s stateside.The piece is a modern showcase, luxuriant in texture and chameleonic in mood; Schrader should have plenty of room to show off the limpid yet precise, slightly theatrical playing that’s made him one of the busiest performers around. He has such range and technique that he can play both as the pianist of the Rembrandt Chamber Players, whose repertoire is heavily 20th century, and as the harpsichordist for the Chicago Baroque Ensemble, whose specialty is pre-19th-century music. Schrader’s also been the organist at the Church of the Ascension on LaSalle for almost two decades, putting to good use his extensive knowledge of liturgical music, and he’s always on call with the Chicago Symphony Orchestra. (He provides the continuo on three of its Solti CDs.) Also on this weekend’s program are John Corigliano’s Elegy for Orchestra (1965), a little-known early exercise in moody lyricism, and Elgar’s Enigma Variations, as deft and intricate as ever but not the crowd pleaser it was before English modernism fell out of favor. The conductor is David Loebel, a promising American talent affiliated with the Saint Louis Symphony Orchestra. Saturday and Sunday, 7:30 PM, Petrillo Music Shell, Grant Park, Columbus and Jackson; 312-742-4763. Ted Shen

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