Wednesday’s ninth chamber program was the first one where I noticed that there were some vacant seats — but not too many. A few more handfuls of listeners could’ve enjoyed another prime program of contrasting chamber jewels.

The afternoon kicked off with Mozart’s K. 493 piano quartet, which — since he wrote it for his own performance — has a particularly meaty and tricky piano part (Wolfgang was quite the piano virtuoso). As director Geoff Nuttall told us, the piece further reflects Mozart’s other penchants as a master of opera and an expert composer of concertos. It’s written in kind of a “concertante” style, with the piano dominating, and it further contains the kind of spontaneous back-and-forth tradeoffs between instruments that are reminiscent of operatic dialogues or ensemble passages.

And it’s also one of Mozart’s better chamber works (not that there are any bad ones). Its sprightly and amiable opening Allegro contrasts beautifully with the exquisite following Larghetto movement, with its surpassing tenderness and lyricism. Pianist extraordinaire Pedja Musijevic  got a particularly stiff workout in the finale: a bracing Rondo that’s full of witty exchanges between the players. Pedja’s “orchestra” consisted of violinist Daniel Phillips, violist Barry Schiffman and cellist Alisa Weilerstein. Pedja further indulged in some improvisatory flourishes, which Mozart was known to do all the time when he performed.