The vibraphone remains one of the most difficult instruments on which to establish a unique or even recognizable style, but Gust William Tsilis is unquestionably doing just that. From a purely technical standpoint his busy, smartly careering lines represent an embellishment on the style of Bobby Hutcherson--a hornlike approach rather than the keyboard-based style of Gary Burton, with plenty of the twists, turns, skeins, and stops found among the best modern saxophone players. That's on the uptempo juggernauts, which he rides as well as any vibist you can name; meanwhile, his slow numbers achieve a dreamlike stasis, even though his solos are unabashedly linear. The most telling clue to Tsilis's success lies in the sturdy, compact ideology that underlies his music. His three most recent albums each sport a different combination of instruments and a unique sensibility, and yet each sounds like a Gust Tsilis creation: credit his ability to focus clearly on a musical goal and then convey that goal to (and through) his bandmates. That ability makes his appearance in Chicago especially worth watching: Tsilis joins a session led by vocalist Kevin Mahogany, which will pair him with Chicago pianist and kindred spirit Steve Million. Based on the music each has made separately, Tsilis and Million ought to really spark; in fact, I expect fireworks. Tonight, Bop Shop, 1807 W. Division; 235-3232.