Commissioned and premiered by Chamber Orchestra of Philadelphia, the concerto was supposed to be 20 minutes long but, in an amiably counterrevolutionary way, occupied 40. Though a single listening in a good but quickly assembled performance probably offered only a fraction of what was there, this is among the more substantial works this 71-year-old composer has written for traditional ensembles. That's "traditional" with an asterisk.

A gurulike figure with a long white beard and a warm, inviting aura, the Bay Area composer is one for the musical competitiveness of conventional concertos. His once-minimalist aesthetic is about layers of unlikely music. And because Riley has gravitated with breathtaking ease toward Indian ragas, the music had a constant sense of alternative possibilities not guided by even the vaguest reference to Germanic classical forms, though the concerto's four movements did sport a fugue and, most moving of all, a funereal version of the 18th-century sarabande.

The three soloists were a heterogeneous resource: Each had solo moments and various combinations of duets, particularly between the guitarists, David Tanenbaum and Gyan Riley. At one point, violinist Krista Bennion-Feeney laid down her violin and picked up temple bells.

At the outset, Riley seemed out to cooperate with the medium, sounding vaguely like Ralph Vaughan Williams, but he soon drilled determinedly toward a desirable but elusive goal with music that's involved, complicated but not convoluted. The second movement was squarely within Riley's world, with non-Western scales used with unison string writing, plus exotic percussion interplay.

The fugue in the third movement was more giddy than severe, while the fourth movement, "Sarabande for Iraq," had oblique references to "Taps," with muted trumpet playing a slow scale that descended into infinity.

The program's Ravel-dominated first half had its breakthroughs. French impressionists don't really need lush string sound (one of my favorite encounters with Debussy's Pelleas et Melisande was with chamber orchestra), and often reveal their Gallic sense of logic without it. That's certainly what music director Ignat Solzhenitsyn was up to with Le Tombeau de Couperin. When string sound was needed, he summoned a forthright timbre that was arresting for not having the typical misty sonic scrim heard in conventional performances.