A new maturity was evident in John McLaughlin's show at the Wax Museum last night. The 40-year-old British jazz guitarist harnessed his dazzling technical skills to the emotional requirements of the songs rather than to the showy requirements of his reputation. Moreover, while his former bands were either all-electric, like the Mahavishnu Orchestra, or all-acoustic, like Shakti, his new band features the best of both. McLaughlin played acoustic guitar exclusively last night but was backed by two Parisians--Katia Labeque and Franc,ois Couterier--on electric keyboards. They created broad, buzzing electric sheets of sound for McLaughlin's pinpoint notes to puncture.

The quintet was completed by French acoustic bassist Jean-Paul Celea and American drummer Tommy Campbell. On the showier pieces, the band picked up McLaughlin's fast, tricky phrases and returned them. The highlight, though, was a new composition, "Blues for Lech Walesa." It opened with slow, melancholy blues passages where McLaughlin's acoustic tone was particularly evocative. It then built to a jubilant swing section, much as Solidarity built to its own climax.

Katia and Marielle Labeque opened the show with delightful duo piano recitals of George Gershwin's "Concerto in F," a best seller for them in Europe, and four Scott Joplin rags. Working from notation, the classically trained French sisters showed pristine precision but were surprisingly free of clutter or daintiness. Grinning at each other across facing Steinways, they gave Joplin's odd syncopations jaunty phrasing and pounded out Gershwin's big climaxes.