The piano duo may be a minor chamber form, but many composers, including Bach and Couperin, have written serious pieces for it. Modern composers such as Stravinsky, Bartok, Poulenc, and Milhaud also have made substantial contributions, exploring the percussive sonorities of concert grands played in tandem. Two of the form's brightest advocates are Ukrainians Alexei Kuznetsoff and Valentina Lisitsa, who met while studying at the Kiev Conservatory in the late 80s. They soon married and abandoned plans for solo careers. Now based in the U.S., they've garnered enthusiastic reviews for their nearly flawless execution and seamless teamwork. At Ravinia three years ago, when they made their local debut as part of the "Rising Stars" series, I was struck by the assured way they handled a couple of 19th-century showpieces, emphasizing their orchestral textures over the intricate fingering. (Their first CD, on Audiofon, confirms my initial impressions.) Their exceptional unity in performance no doubt derives from hours of practice, but it also epitomizes the intimacy of most other memorable duos, which have tended to be spouses, lovers, or siblings. For their third visit to Chicago, Lisitsa and Kuznetsoff have chosen a less frivolous sampler than usual. Instead of Liszt and Rachmaninoff, they offer a Mozart classic, the understated and structurally interesting Sonata for Two Pianos in D Major. The closest thing to 19th-century Romantic bombast is the Suite no. 1 in G Major by the obscure Russian composer Anton Arensky, which includes passages of Tchaikovskyan lyricism. The rest of the program is given over to 20th-century French entries, from a transcription of Ravel's La valse to Milhaud's Scaramouche to Poulenc's Sonata for Two Pianos. The Ravel is tricky for any duo to negotiate, and the elegant, melodious Poulenc requires the lightest of touches, something not within the grasp of many duos. Friday, 8 PM, Mandel Hall, University of Chicago, 1131 E. 57th; 773-702-8068.