The five members of the Orion Ensemble, founded in 1992 and now in residence at Roosevelt University, play with great technical assurance and musicality. They gave an outstanding performance of Shostakovich's Trio no. 1 in November, and their gusto and wonderful phrasing can be heard in their new CD of lesser-known contemporaries of Brahms. Their unusual combination of instruments--violin, viola, cello, piano, and clarinet--gives them a remarkably wide range of repertoire possibilities, from Mozart to Messiaen and beyond, and they're committed to performing unusual works and new commissions. For this program they'll play Charles Ives's short Largo for violin, clarinet, and piano--an absolute gem. The gentle lullabylike outer sections have lovely solos for the violin and clarinet, and the middle section is full of sudden outbursts of ragtime. In honor of Mozart's 250th birthday the group will perform his Trio in E-flat, K. 498, for piano, clarinet, and viola, which he wrote while playing skittles. This is elegant music, with three moderately paced movements that are sometimes playful, sometimes somber, and the gorgeous contrapuntal writing keeps the viola and clarinet from obscuring each other. Also on the program is Black Tango, a 2002 work for violin, viola, cello, and piano by American composer Erling Patrick Horn, and Debussy's Trio in G for violin, cello, and piano, written when he was just 18 and not discovered until the 1980s. Reconstructed from several sources, it's very romantic and at times contrived--definitely not his finest work, though it does have kernels of his later ideas, such as parallelisms, repeating motifs, and contrasts between the delicate and the lush. On Sunday, March 19, the ensemble plays in Batavia; see separate Treatment item for details. Wed 3/22, 7:30 PM, Ganz Hall, Roosevelt University, 430 S. Michigan, 630-628-9591, $23, seniors $20, students $8, children under 12 free.