Starting a program with Pierre Boulez, that paragon of cerebral modernism, and ending it with Balinese ensembles and dancers is your basic day at the office for Orchestra 2001, the Swarthmore-based modern-music ensemble that shrinks from little. The unexpected part of Saturday's concert at the Philadelphia Ethical Society was when these disparate elements melded, seemingly by accident, and then, amid better-laid plans, did not.

Boulez was represented with 1984's Derive I, a 10-minute chamber piece for winds, strings, and percussion that, we can see in hindsight, is an instance of seemingly repressive systematization yielding something that sounds like complete musical freedom. Written with Boulez's typical clarity and density, it often feels like an exotic rain forest of ideas — and under James Freeman's direction, a somewhat violent one — though with the planning of a topiary garden.

Boulez may be light-years away from Bali conceptually, but it didn't feel distant at all when followed by Gerald Levinson's 1981 Black Magic/White Magic song cycle (written in Bali) and then the Gamelan Semara Santi ensemble.

The Levinson cycle has the best of several worlds: The composer took all the right cues from his wife Nanine Valen's poems with intuitively fashioned vocal lines that work selflessly to make the words reveal their surface meaning and inner poetry. The instrumental writing hails from a time when atonality was still the way to go. Some passages sound like Bach in an anti-gravity chamber. Words suggesting haiku-like nature studies are characterized by wind solos bristling with the chaotic harmony of tropical nature and by dramatic explosions of string pizzicatos.

Other songs are quirky parables with contrasting vocal line and instrumental writing, which creates a dichotomy allowing the two entities to comment on each other from separate spheres. Each song takes on its own compositional problem with great invention, including the cycle's charming bookends: a winning instrumental prelude and a spoken conclusion. Mezzo-soprano Freda Herseth handled all challenges with authority.

The program's second half, with the Gamelan Semara Santi group, was problematic if only because these metallic, outdoor percussion instruments were in the small, indoor Ethical Society auditorium. To the unschooled ear, it was like descending into the metal workshop of Wagner's Das Rheingold, when, in fact, these Balinese works are layered with meticulous sophistication.

With his new piece Inside/Outside, composer Thomas Whitman, who founded the gamelan ensemble, attempted to bring together his traditional instruments with the ensemble that Boulez built. With the two groups in full cry, the balance problems were hopelessly weighted toward the outdoor instruments. But when Whitman broke down both ensembles into incidental solos, meaningful interactions were indeed possible.

Contact David Patrick Stearns at dstearns@phillynews.com.