Two of the burningest Zairian soukous acts are visiting Chicago within the next two weeks; this weekend it's Zaiko Langa-Langa, who've been at it through various personnel changes since 1971. A recent LP on the Espera label from France reveals Zaiko to be a big, rich-sounding ensemble whose forte is lilting harmonies that build inexorably toward the requisite six- to eight-minute dance break. To my Western ears they share more with the old Congolese masters--Tabu Ley Rochereau (who gigged in Chicago last month) and the late Franco--than they do with more recent revved-up innovators like Diblo and the Kanda Bongo Man (coming here next week). The younger bands ditch the sweet balladry in favor of a harder, faster dance beat; Zaiko still plays it pretty, and their rhythmic groove retains a hint of unhurried grace that always sounds nice after a few hours of American R & B and rap. Be sure to wear comfortable shoes--this dance party could run pretty late. Saturday, 10 PM, International Longshoremen's Association Hall, 1307 S. Michigan; 334-2293, 275-2626, 989-4440, 955-7742, or 784-4608.