Though his name recalls Germany's most famous musical tribe, Michael Bach claims no direct blood ties to the great J.S. Not that it matters. The cellist extraordinaire, at age 33, can stand on his own right as a virtuoso and as an avid champoin of contemporary chamber music. Classically trained--under the tutelage of Pierre Fournier and Janos Starker--Back decided on his present specialization in the mid-70s after a summer at Darmstadt, one of the hotbeds of experimentalism. These days, he's noted for the intensity and immediacy of his performance and a dedication to new music so fierce that composers on both sides of the Atlantic eagerly seek him out for collaboration. In his Chicago debut (sponsored by the Goethe-Institut Chicago) Bach will offer a survey of the high points of the post-50s literature for solo cello: John Cage's Music for One (1984), Projection I and Intersection IV (1953) by Morton Feldman, Solosonate (1960) and Four Short Studies (1970) by the German iconoclast bernd Alois Zimmermann. In the (superb-crafted) Zimmermann pieces, which I've heard, the cello is a Beckettesque solitary wanderer in a world of anxiety and despair: it grunts, gorans, moans, wails as if trying to articulate the modern man's emotional predicament. Technically difficult, they demand the utmost mental concentration and nimbleness from the cellist. The program's lone golden oldie is J.S. Bach's D-minor Cello Suite; it will be performed with a curved bow, which is patterned after the arched bow used during the 18th century and supposedly allows for the rapid exchanges in counterpoint intended by Baroque-era composers. Bach's cello is a rare Maggini (circa 1590), a gift from mentor Fournier. Tonight, 6 PM, Goethe-Institut Chicago, 401 N. Michigan; 329-0915.