Cutting-edge music declared too difficult to perform was, in the past, sent to Leopold Stokowski, who didn't need to understand pieces to conduct them convincingly. Now, conservatory students such as the Curtis 20/21 ensemble pioneer the unperformable, in this case

Siddhartha's Dream

by David Shapiro. From the Perelman Theater stage Sunday, the composer claimed this ensemble was among the few that could hope to handle it.

Meditation music, it's not. Commissioned for the concert and presented in a laudable partnership with the Philadelphia Chamber Music Society, the piece attempts to portray the Buddha's ability to see all of mankind at once - all seven billion of us. The piece circled the world in 18 minutes, each orchestral section having a sliver of a showcase, all from different harmonic universes that have only their anarchy in common, ending with a wild piano cadenza suggesting Stravinsky on crack.

Or so it seemed on first hearing. Though solid, the performance under conductor David Hayes had momentary insecurity. Wouldn't musicians and listeners benefit from a repeat performance at some later concert? It could be the perfect encore.

Elsewhere, Curtis 20/21 followed no single agenda. The two Latino composers bore little resemblance to each other. Osvaldo Golijov's 2010 Sidereus was in his spacious film-score manner, with long-breath, Mideastern-inflected melodies unfurling over minimalist-influence rhythms.

Roberto Sierra's 2006 Concerto for Viola, heard in its U.S. premiere, is among the composer's more brooding, atmospheric, and substantial works. Unlike past pieces, his ideas weren't buried under excessive notes. Soloist (and Curtis president) Roberto Diaz gave the most electric performance I've heard from him since he left the Philadelphia Orchestra in 2006.

The program's one classic was Lukas Foss' 1960 Time Cycle for soprano and chamber group. Foss set to music provocative meditations on time by W.H. Auden and Franz Kafka, illustrated by the piece's structural process more than by its surface rhetoric. Soprano Anna Davidson made the vocal lines sound as intuitive as possible, acting like a beacon amid the rushing sands of time. Greater dramatic involvement would've been preferable - plus a more pronounced sense of jazz among the instrumentalists.