In terms of unbridled trumpet power, Orbert Davis brooks little competition in Chicago. So what's he doing with a 10-piece string section? (It's actually 11 if you count bassist Marlene Rosenberg.) Some jazz musicians have worked with strings in a misguided effort to "legitimize" their music; others have chased a genuine fusion of forms, in which the orchestra colors and interacts with the improvisations. For Davis the strings serve the same purpose as in Charlie Parker's famous recordings with similar instrumentation: they boost and frame his spotlit solos in all their impressive extravagance. Indeed, some of the original arrangements used by Parker are included in Davis's repertoire. But Davis has also penned several of his own; they include a provocative version of "Stardust" and well-chosen tunes of more recent vintage, and they make this string section's book a lot hipper than you'd expect. Against this backdrop, Davis strives for the gorgeous--the "showily brilliant" in the dictionary denotation of this often misused adjective--and he usually succeeds. Davis excels in many contexts, from his own postbop quintet to William Russo's repertory big band, but for pure emotionalism and finger-busting fireworks, nothing comes close to this. In fact, as he soars above the strings' springy support, Davis's trumpet becomes splendiferous--gleaming gold against the earth tones of violins and cellos. In so doing, he expertly treads the line between virtuosity and excess, inviting the ghost of Harry James to sit with Freddie Hubbard and Clifford Brown in the circle of Orbertal influences. The group will sound their best this weekend, fresh from a crowd-thrilling performance at Monday's Jazz Fair. Saturday, 8 PM, Green Mill, 4802 N. Broadway; 878- 5552.