Crossover projects in classical music have traditionally been matters of opera singers or big-ticket instrumentalists performing jazz, pop or folk music, usually not as well as the musicians who perform this material full time. But since the late 1980s, crossover has moved in the other direction too. Stewart Copeland and Roger Waters have written operas; Paul McCartney has written a stream of orchestral, choral and piano works; Elvis Costello has composed a ballet; and Sting -- Copeland's onetime colleague in the Police -- has undertaken several performance projects, most notably 'Songs From the Labyrinth,' a 2006 CD of John Dowland songs and lute pieces, performed with a pop singer's freedom and unpolished vocal tone. You could easily fault him for those qualities, but in interviews Sting has made it clear that he is aware of his shortcomings. And he has discussed Dowland's songs, and other classical works, with a passion that shows that his heart is in the right place: He loves this music and wants people to hear it. That was presumably part of the thinking behind 'Twin Spirits,' a 100-minute hybrid theater piece and concert in which Sting and his wife, the actress Trudie Styler, appeared on Wednesday evening at the Allen Room. The work, written and directed by John Caird and first performed at Covent Garden in 2005, is meant to bring to life the romance between Robert and Clara Schumann. A 2007 performance, also at Covent Garden, has been released as an Opus Arte DVD. Sting makes no attempt to sing Schumann's lieder in this production; the vocal music is the province of a baritone and a soprano. Instead Sting portrays the composer, reading from his letters to Clara Wieck during their long courtship and from the joint diary they started when they married in 1840. Styler plays Clara and reads her end of the correspondence. Not much acting is called for. Sting and Styler remained seated through most of the production, but to their credit, they endowed the Schumanns' letters with a sense of the emotion behind them: amusingly in the case of Schumann's playful, mildly eccentric early missives; poignantly when Clara reports on Schumann's madness, institutionalization and death. A narrator, David Strathairn, filled in the details, chronology and context from a thronelike seat on a platform behind Sting, Styler and the six musicians who performed music by both Schumanns, with a sprinkling of Chopin and Mozart, between groups of letters. Caird's script is efficient and fast paced, though toward the end, when Schumann's correspondence dries up as his mental afflictions take over, the text necessarily shifts toward narrative, and the musical sections grow longer. That was not a problem. As hard as 'Twin Spirits' works to build a sympathetic audience for the Schumanns, in the first two-thirds of the piece, the music -- the point of Schumann, after all -- is too often incidental. Some works are reconfigured to no great purpose. The 'Preambule' to 'Carnaval,' presented as an introduction to the epistolary dialogue, begins as the keyboard piece Schumann wrote. But Jeremy Denk, the pianist, has only a few bars to himself before the work morphs into a piano trio, with the violinist Joshua Bell and the cellist Nina Kotova joining in. Another 'Carnaval' movement, 'Marche des Davidsbundler Contre les Philistins' is given a more theatrical rescoring, with passages alternating between, on the one hand, Denk and Bell, and on the other, Kotova and a second pianist, Natasha Paremski. The idea, clearly, was to create an exchange between male and female pairs of musicians. Similarly, 'Traumerei,' from 'Kinderszenen,' was transformed from a solo piano work into a dialogue between Denk and Paremski. The 'Traumerei' arrangement was innocuous, and the two pianists matched their sound and phrasing nicely. But in the 'Marche,' the tension of the piano writing was sacrificed in translation. That said, the performances were often strikingly beautiful. The baritone Nathan Gunn, supported by Denk, sang exquisitely shaped, comfortably confidential accounts of three songs from 'Dichterliebe,' offered without interruption toward the end of the show, as well as a gently introspective reading of 'Stille Liebe' from 'Zwolf Gedichte.' Camille Zamora, the soprano, accompanied by Paremski, gave a dramatic, shapely reading of 'Er ist gekommen in Sturm und Regen and Zamora and Gunn collaborated affectingly on a graceful performance of 'La ci darem la mano,' from Mozart's 'Don Giovanni' (included because Robert gave Clara a copy of the score as a gift). A section from Chopin's variations on 'La ci darem' was included too, as another pianistic dialogue between Denk and Paremski. With Kotova playing a one-line reduction of the orchestra part, Paremski made a strong case for the Romanze from Clara Schumann's Piano Concerto No. 1. And Bell applied his characteristically sweet tone to the second of Schumann's Opus 94 Romances. It is easy to see 'Twin Spirits' and shows like it as Music Education Lite. But part of the point here was to raise money for the real thing. Some of the proceeds from the Wednesday evening performance (and several earlier ones) will go to Music Unites, an organization that underwrites music education programs for underprivileged children. 