Although Kopernikus was completed in 1979, it received its US debut only in 2016 and didn't reach New York until last year. Both productions were directed by Sellars, who was introduced to Vivier's music by Dutch contemporary music specialist Reinbert de Leeuw.
"Reinbert worked with Messiaen, Stockhausen, the most incredible composers," says Sellars, "but he said to me quietly, 'You know, I think the greatest composer whose music I've played is Claude Vivier.'"
Vivier's music – Kopernikus in particular – is achingly beautiful. Thinly scored for seven singers and seven instrumentalists, the opera, according to Sellars, represents Vivier's imagined journey from life, through death and into new life, gently increasing in intensity and complexity as the work progresses.
It's a tuneful, almost hallucinatory listen, with nothing to scare the audience musically, so perhaps Kopernikus's obscurity is down to its plotless life/afterlife themes that can veer perilously close to New Age drippiness. Then there's Vivier's insistence in setting it in three languages - French, German, and his own made-up "magic speech" - and the characters that pop up, including Mozart, Lewis Carroll and Merlin.
However, Sellars doesn't think that's why Kopernikus has been ignored: "I just think some people live and die without being recognised. The history of classical music is full of people who are only recognised after they're gone; Vivier's a poignant example of that. I also think his music is way beyond fashion. It was not what French avant-garde music was in the 1970s and 80s; he was out of step completely and we're just getting around to him now."
The same could not be said of Sellars, who, whether loved or loathed, has been at the top of his profession for 40 years, originally forging his name by creating iconoclastic versions of the classics. Sellars's Don Giovanni was notorious. Set in a New York slum, he made his title character a drug addict and rapist, while in one early scene, Donna Anna shoots up on stage and proudly displays her needle marks.
But Sellars thinks Mozart's music is tough enough to handle this kind of treatment.
"For me, the definition of a classic is something in which every generation sees its own story," he says. "If something needs to be set in its 'proper' time, then clearly it's not a masterpiece. Wherever you set Mozart or Shakespeare, it's going to illuminate everything it comes into contact with. And to borrow a phrase from indigenous people, it's also a way of measuring ourselves against our ancestors, and inviting our ancestors into the room; it's interesting to have Mozart and Shakespeare comment on how we're living."
That approach has not always found favour. Elisabeth Schwarzkopf, perhaps the greatest Mozart soprano of last century, famously refused to let the director's name be uttered in her presence, accusing him of "spraying graffiti over masterpieces".
Schwarzkopf was not alone in her appraisal but Sellars again insists he's not annoying people for the sake of it and that "shocking the bourgeoisie" is of no interest to him. What does interest him, then?
"You're just trying to be useful," he says, bursting into laughter. "Every day you wake up and say, 'What's missing from this picture? What are people not seeing, not hearing, not saying?' Then you look around and what you don't see is what you put there."
Lowdown
What: Peter Sellars directs FLEXN, Claude Vivier's Kopernikus and Orlando de Lasso's, Lagrime di San Pietro.
Where & when: Te Rauparaha Arena, Porirua, February 23 and 24; Opera House, Wellington, March 1 and 2; Auckland Town Hall, March 13.
