It's easy to see tap dance as monochromatic--yet variety is what makes Mark Yonally's new company, which consists of him and nine women, appealing. It's not surprising that in his choreography Yonally uses such musical principles as canon, unison, and syncopation. But add the visual interest of the dancers' arrangements onstage and their interactions, whether they're looking over their shoulders at a solitary figure or leaning together in a companionable group, and you get a satisfying mix of aural pleasures and the emotional pull of dance theater. In Motherless Child, set to Mocean Worker's trip-hop version of "Summertime" and premiered last fall during Dance Chicago, the company creates a thunderous noise while evoking a subtle story and occasionally pausing in graceful poses atypical of tap. The effect is almost surreal, both military and soft. In other cases--as in Moose the Mooche, set to the Charlie Parker song of the same name--the dancers are more conventionally entertaining, apparently enjoying nailing the beat, then embroidering on it. Half the program is set to recorded music, mostly bebop and trip-hop, while the other features a live jazz trio. Yonally performs the occasional solo, including Mercy, Mercy, Mercy, which showcases his light, rapid tapping to a live funk-jazz version of the 1967 tune. Performed in a chamber setting--a studio space at the Athenaeum--this promises to be an intimate, heart-rattling experience. The performance on Saturday (National Tap Dance Day) also features Chicago artists M.A.D.D. Rhythms, Especially Tap Chicago, Rhythm I.S.S., and Perfect Timing; it's followed by a tap jam, so bring your dancin' shoes. For Sunday's performance Chicago Tap Theatre will be joined by two youth companies, Footprints and Visual Rhythm. Athenaeum Theatre, second-floor studio theater, 2936 N. Southport, 312-559-1212. Through May 26: Thursday-Saturday, 8 PM; Sunday, 3 PM. $10-$18; the May 25 show is $15-$25.