In contrast to the standardized splendor of the modern symphony orchestra, new-music groups have to be loose collectives if they're to take the alternative shapes and forms insisted upon by boundary-pushing composers.

Network for New Music went particularly far afield in a Stravinsky/Hindemith/Ligeti program in a wildly unexpected cast of characters: Eminent pianist Leon Fleisher, now 80, conducted some of the craziest vocal music yet written, with musicians imported from Baltimore's Peabody Institute, where he's on the faculty. What an exhilarating concert it was. Clearly, the Philadelphia Chamber Music Society (which presented it) isn't letting cobwebs form on its subscribers.

Ligeti (1923-2006) eventually came into the symphonic fold by writing concertos - albeit so dense as to defy memorization, forcing soloists to read their music off electronic screens operated by foot pedals. The younger mid-1960s Ligeti was heard Monday at the Perelman Theater, specifically Aventures and Nouvelles Aventures for chamber ensemble and a trio of vocalists using artificial language. Some of it sounded like baby talk; there were many variations on panting. Sounds were sung, shouted, and excreted, suggesting the Ray Conniff Singers with an aggressive case of Tourette's.

Coached by Peabody's new-music doyenne, Phyllis Bryn-Julson, the vocalists (Bonnie Lander, Diane Schaming, and James Rogers) had such an expressive directness that conventional words would have gotten in the way. Their petulent performances gave the high-velocity pieces an A-to-Z emotional range with expediency and brevity, unburdened by the linear plots of operas. Even though both Aventures have transcended their experimental status, wasn't one enough? No. They brilliantly build on each other and must be heard together.

Having pursued a side-career in conducting for decades, Fleisher delivered solidity, clarity, and heat that was especially apparent in non-Ligetian moments that had him working with an ensemble drawing heavily from the Philadelphia Orchestra.

Stravinsky's 1954 In Memoriam Dylan Thomas was played twice because its compositional intricacies are so subsumed by the music's elegiac purpose, and Hindemith's 1922 Kammermusik No. 1 (Op. 24) handily bridged the worlds of cabaret, concert music, and Dada-ist art thanks to an ensemble augmented by accordion and police siren. Hindemith's best moments, though, lay in the spare, distilled writing of the third movement, with woodwinds in oblique dialogue with bells.