On a bright, airy classroom on the West Side, six youngsters are grooving to Miles Davis, their feet gently tapping, their bodies swaying a bit as they savor the trumpet sighs wafting out of a portable stereo system. Meanwhile, at the tony Symphony Center downtown, a much larger group of kids is hanging on to every note that jazz trumpeter Wynton Marsalis is playing, as he re-creates the clarion sound of Louis Armstrong hitting a glorious series of high Cs. The day's topic may be vintage Mil …