Alexander Kobrin's concert Friday night at the Kaye Playhouse at Hunter College featured the kind of artful, sensitive playing that one hears with less and less frequency on concert stages these days. Perhaps the greatest success of this performance was his astounding tonal control-- showing complete command and mastery over every touch, from the quietest to the most dramatic-- yet never creating sounds that were harsh, ugly, or unpleasant. Mr. Kobrin was the Gold Medal winne