Just after intermission and before a performance of Mozart's A Major Quintet Sunday afternoon in Auer Hall, esteemed clarinetist James Campbell introduced his playing partners, the Avalon Quartet. Even though its members looked very young, Campbell insisted that they had been a busy touring ensemble for some time. Two, he said, had studied with IU's Mauricio Fuks, adding that the four had all now become residents of the state because they've been named the resident string quartet at Indiana University. Campbell paused teasingly, then noted, "South Bend." So, no big hiring news for IU Bloomington but, said Campbell smiling, "We can have them back again as visitors." They're worth inviting back. They cause their instruments to emit very musical sounds, and they play fluidly as a team, and - if the Mozart that followed and some Janacek that came before are representative of what they can do with chosen scores - they bring a shared perception to the stage. How fortunate, of course, for them to have had Campbell as their collaborator in the A Major Quintet. He set the expressive character for the reading, giving the delicious opening a sense of buoyancy that the five musicians held on to throughout. Their way with the radiant second movement, the Larghetto - muted strings in contrast with the lyrical clarinet - imbued the music with a honeyed blend of lightness and longing. The Avalon (violinists Blaise Magniere and Marie Wang, violist Anthony Devroye, and cellist Sumire Kudo) scored also with Leos Janacek's 1923 Quartet No. 1, subtitled "Kreutzer Sonata," after the Tolstoy novella about jealousy and marital misery. Each of its movements contains the instruction "Con moto," meant to tell performers to supply animated and energetic movement. The visitors did just that. Their interpretation also was intimate, ardent, suffused often with a hint of mystery and shadows. The program began with more Mozart, the Trio in E-Flat Major for Clarinet, Viola, and Piano, "Kegelstatt," named so, according to legend, because while composing, Mozart also played "Kegelstatt" or "Skittles," a game much like bowling. Well, whether he did or not, the music that resulted is a delight, made all the more a pleasure to hear on Sunday because of the gifted lineup of artists: Campbell on the clarinet, Paul Biss on viola, and Jean-Louis Haguenauer at the piano. What one heard was beguiling, no less.