Greatness can sometimes hold musicians hostage.

Just because classical music offers a shot at a renewal experience with every performance doesn't mean everyone will seize that opportunity as the decades go on. After 30 years, the venerable Moscow Quartet has more mileage on it than a fleet of UPS trucks, which was all-too-audible in their performances Sunday of often-played cornerstones of their repertoire by Haydn and Schumann. Instead of drawing accumulated wisdom from the tattered pages on their stands, the players seemed to have forgotten what makes these works sing.

But before any assumptions about burnout could be made at this Convention Center concert, the presence of guest pianist Ignat Solzhenitsyn put the quartet on new-ish ground with the less-often-heard Franck Piano Quintet. More personal musical engagement took precedence over nondescript tone quality and technical missteps that were too noticeable in the first half. Though the first chord had a raspberry from first violinist Eugenia Alikhanova, the opening thematic statement was phrased with such an organic sense of gravity, you felt floodgates of emotion opening up.

Typically, the piece is played with Gallic elegance. However, this is one of several Franck chamber works that have Wagnerian scope in a medium that Wagner himself never got around to. The performance served that grandeur, though the plaintive loneliness that Alikhanova gave to her second-movement solo was so right, so intimate, it's bound to become a permanent part of my performance memory of the piece.

Though Solzhenitsyn's career conducting the Chamber Orchestra of Philadelphia demands authoritarian music-making, he was a willing ensemble member here, working within the string texture as well as stepping out of it in thoughtful incidental solos. Considering how lethargic the Moscow Quartet can be on its own, he's probably responsible for the coiled-spring tension that propelled the music from one paragraph to the next with mounting brinksmanship. Chamber music shows him at his best, showcasing his originality while tempering his excesses; one is grateful to the Philadelphia Chamber Music Society, which presented the concert, for contriving such opportunities.

Haydn's String Quartet Op. 64 No. 5 ("Lark") and Schumann's String Quartet Op. 41 No. 3 are usually good to hear under any circumstances. But when the sluggish, all-too-episodic performances suggest the musicians are at the end of their road with this music, everybody would benefit from taking risks with less popular works. The Moscow Quartet has a valuable history with such 20th-century masters as Alfred Schnittke and Edison Denisov. They're ripe for revisiting - while the quartet still has the vigor to do so.

Contact music critic David Patrick Stearns at dstearns@ phillynews.com. Read his recent work at http://go.philly.com/ davidpatrickstearns