I was intrigued but not impressed by the Orion Ensemble in their early days. Their unconventional mix of instruments--violin (Florentina Ramniceanu), viola (Marlise Klein), cello (Judy Stone), clarinet (Kathryne Pirtle), and piano (Diana Schmuck)--allowed for flexibility in repertoire, and their all-female lineup was something of a novelty a decade ago. But they didn't always play with cohesion and balance: the piano sometimes overwhelmed the other instruments, and the violin intonation was errant. Lately, though, the playing has been tighter and the teamwork more disciplined; they've developed an understanding of how to shape a performance, and, more often than not, they agree on a convincing interpretation. Their improved skills and their penchant for uncovering neglected items and seeking out commissions (from the likes of Chicagoans Augusta Read Thomas and Sebastian Huydts) have elevated the quintet of busy freelancers into a reliable chamber group. (In 2000 Orion, now affiliated with Roosevelt University as the ensemble-in-residence, won the Chamber Music America/ASCAP Award for Adventurous Programming.) Every program guarantees at least one discovery, and in the latest series of recitals it's the Quartet in F for Clarinet and Strings by Johann Baptist Wanhal. An 18th-century Bohemian contemporary of Haydn, the prolific Wanhal isn't well-known today, but clarinetists like Orion's Pirtle think of him fondly because he was among the first to write for the instrument. The piece exploits the clarinet's timbre and lyrical quality in the graceful manner that marks the early classical style. The showstopper, though, is bound to be Bartok's Contrasts, a seminal work noted for its blending of jazz and classical elements. It was written for Benny Goodman, violinist Joseph Szigeti, and pianist Endre Petri, and that's a gold standard for Pirtle, Ramniceanu, and Schmuck. Beethoven's Archduke Trio rounds out a program for which the term "challenging" isn't an overstatement. Sunday, November 24, 3 PM, Winnetka Presbyterian Church, 1255 Willow, Winnetka. Sunday, December 8, 7 PM, Fox Valley Unity Church, 230 Webster, Batavia. 630-628-9591.