This group should have been called "Sons of Stockhausen," including as it does in its lineup two sons of the famous (some would say infamous) avant-garde German composer Karlheinz Stockhausen. As it is, the name is not only a polemic against the popular Kronos Quartet but an indication of the way that the group approaches time in its improvisations. There is no set form or structure to the music, simply intuitive momentum. The result is an unusual pastiche of sounds that run the gamut from the latest in new-music electronics to German bebop, fusion, even pop. Leader Markus Stockhausen's guiding trumpet comfortably sways between a Miles Davis kind of cool, Ivesian ambiguity and Copland brilliance. The ensemble, which is made up of five players who at one time or another play trumpet, saxophone, trombone, piano, drums, percussion, and synthesizers, are full of fascinating musical ideas that they are willing to explore in performance, regardless of where it might take them stylistically, rather than jump quickly from one idea to another, as is so common in improvisatory groups. Sponsored by the Goethe-Institut and Southend Musicworks. Tonight, 8 PM Arts Club of Chicago, 109 E. Ontario; 667-1469 or 329-0915.