Among Spoleto’s unheralded (and overworked) heroes are the members of the Spoleto Festival Orchestra. They’re carefully chosen each year from America’s best music schools to create Spoleto’s “orchestra of virtuosos.”

They also do some heavy multitasking while here, providing music for the festival’s operatic and choral productions, as well as the Intermezzi and Music in Time series. But their best moments come with their customary pair of headline orchestral offerings under Maestro Emmanuel Villaume. They’re also a key ingredient to sacred choral guru Joseph Flummerfelt’s big choral-orchestral extravaganza.

Your first chance to hear them will come with Gustav Mahler’s Das Lied von der Erde (Song of the Earth), a monumental cycle of six orchestral songs for tenor and alto soloists based on ancient Chinese poetry. Thus continues Villaume’s intermittent Mahler symphonic “series” (Symphonies Nos. 4, 5, and 9) that has spread across recent festivals.

Though formally billed as a song cycle, Mahler buffs tend to think of it as a symphony. Its six songs can be easily lumped into a four-part “symphonic” sequence. The opening “Drinking Song of Earth’s Sorrow” stands alone as a fevered paean of dark, unyielding grief in the face of mortality. The slow movement comes with “The Lonely One in Autumn,” with its bare orchestral lines underscoring the poet’s bitter disillusionment. Three shorter songs bring contrasting lighter moods before “The Drunk in Spring” closes the interlude. This is a favorite Mahler work of many. We’ll hear the remarkable mezzo-soprano Sasha Cooke and tenor Russell Thomas. Their virtuosity allows them to play anything well, so all Villaume has to do is hold his band of musical tigers by their collective tail.

Two more works await us in the next orchestral event, beginning with Johannes Brahms’ deep and soulful Violin Concerto in D Major. It’s a big, often dramatic bruiser of a concerto that’s about as far removed from a flashy, shallow showpiece as you can get.

And that’s exactly how mega-violinist Sarah Chang, the evening’s soloist, approaches this work. She first learned it as a child, but set it aside for over 10 years before taking it up again. And it remains one of the few major concertos she hasn’t yet recorded.

Still, it’s one of her three favorite concertos, and her personal Everest. Her precious instrument, a 1717 Guarneri del Gesu, should make Brahms’ frequent lower notes sound especially rich and juicy. This’ll be Chang’s first Spoleto appearance.

The evening’s blockbuster will likely be Tchaikovsky’s Symphony No. 6 in B Minor, a work of gut-wrenching contrasts that, while composed during a burst of happy creative drive, was premiered just days before Tchaikovsky’s death. Villaume and company are equipped to wring every last scream, sigh, and sob out of this amazing score.

On to the festival’s big choral-orchestral evening, where a smaller Spoleto Festival Orchestra will join Maestro Flummerfelt and his superb hybrid choir of Westminster Choir singers plus members of our own Charleston Symphony Orchestra Chorus. The magnum opus here is Mozart’s Requiem in D Minor, which he left unfinished at his untimely death. While up to four different composers may actually have had a hand in its eventual completion, we’ll hear the usual version that’s attributed to Mozart’s pupil, F. X. Süssmayr. Joining the fray here will be a top-notch quartet of soloists (all from Louise): Soprano Anne-Carolyn Bird, mezzo-soprano Marjorie Elinor Dix, tenor Mark Thomsen, and bass Stephen Morsheck.

Flummerfelt and company will take us out with Francis Poulenc’s compact Gloria, a mysterious and affecting piece that reflects the composer’s deep Catholic faith, while indulging in his hallmark touches of humor and whimsy. Just wait until you hear soprano soloist Kiera Duffy deliver the stratospheric, spine-tingling “Domine Deus” aria. Sheer magic.