The Chicago Symphony Chamber Players are a small, flexible group anchored by violinist Samuel Magad, who's still going strong after 30 years as concertmaster of the Chicago Symphony Orchestra. Despite their shifting lineup (though they sometimes number a dozen or more, for this weekend's performance they've pared down to five), the Chamber Players rarely waver from the level of commitment and quality one expects from CSO veterans. From time to time it's possible to tell they haven't squeezed enough rehearsal time into their hectic schedules--it's one thing to play together in a full symphony, and quite another to be required to respond to one's fellow musicians at close quarters, without the benefit of a conductor. But even underrehearsed, this is an excellent chamber group; at this recital they'll showcase CSO French horn principal Dale Clevenger in a pair of horn quintets and perform half of a four-part string quartet called Sun Threads, by CSO resident composer Augusta Read Thomas. Thomas's recent orchestral music is distinguished by an opulent sound and constantly morphing textures and timbres, and her chamber works--though by necessity not as grand in scale--have the same combination of forcefulness and delicacy. "Invocations" and "Fugitive Star," the two movements on the program here, were both composed in 2000, though for different occasions. "Invocations" is playful and spunky, its gestures gradually becoming more percussive and piquant; in "Fugitive Star" the viola begins lyrically, then leads the rest of the quartet into a series of bold paroxysms that bring to mind the cosmological imagery Thomas loves so much. She seems to be maturing as a composer, resisting faddishness (minimalism, neomedieval mysticism, quotations from pop music) and growing more comfortable with her own voice. One of the horn quintets is the Mozart; the other, a pleasant neoclassical exercise by Bernhard Heiden. And Clevenger, who's held his post at the CSO even longer than Magad, is one of only a handful of horn players in the world with the stamina and finesse to tackle both in one program. Sunday, April 7, 2 PM, Fullerton Hall, Art Institute of Chicago, Michigan and Adams; 312-294-3000 or 800-223-7114.