The Chicago Ensemble's eclectic programming is designed in part to rotate the spotlight on its members, whose reputations as solo performers are all solid. Taking their turns in the latest round of concerts are clarinetist Charlene Zimmerman and soprano Doris Kirschner. For Zimmerman, Bartok's Contrasts poses a formidable challenge: the breathtaking virtuosic passages were written for Benny Goodman, who premiered this jazz-influenced, strongly Hungarian showpiece in 1940 with violinist Josef Szegeti and Bartok himself at the paino. For Kischner it's Downtown Blues for Uptown Halls (1977), a Gershwin-esque song cycle by New Yorker Jack Gottlieb, a disciple of Aaron Copland better known for his musical settings for Jewish religious texts. Inspired by the image of a lonely flophouse and its barely flickering neon sign, the trio of ballads--"Big Little Girl," "Impulse," and "Neon Light"--evoke the sad, existential mood of film noir. The same instrumental combo--voice, clarinet, and piano--will also be on hand for the willfully romantic German Songs (op. 103) by Ludwig Spohr, the cut-rate Schubert. The program's remaining item allows both Kirschner and Zimmerman to take a breather: Beethoven's furiously sunny Sonata no 7 requires the services of pianist Gerald Rizzer and violinist Liba Shacht only. Sunday 3 PM, International House, 1414 East 59th. 509-9031.