"They'll be making their entrances and exits in Tristan," Stier explains. "And when somebody is killed, the body will be staying there on stage. I remember Heiner Muller's fairly minimal production of the opera at Bayreuth in 1995. I could compare that one to ours very simply," he laughs. "In Bayreuth, the orchestra was in the pit while we'll be on stage and, in Auckland, the house lights will be on rather than off."
Stier first heard the music of Tristan und Isolde as a teenager.
"I was 14 and my friend brought over some LPs of Tristan and Scriabin," he recounts. "It certainly proved an interesting evening. What made the most immediate impression with Tristan was what sounded like musical ecstasy, delirious almost to the point of madness."
Now, when asked for a recommended recording of the opera, he has no hesitation in picking out Carlos Kleiber's 1980s set with Rene Kollo and Margaret Price as the doomed lovers.
"Kleiber is always striving," Stier stresses. "He pushes the tempo through all those exciting passages; and sometimes you feel you're in danger of going mad if you get too close to it."
We broach the issue of sexuality and I mention how Clara Schumann was utterly repulsed by Wagner's opera, deeming it the most disgusting thing she had ever heard or seen.
Stier smiles. "Oh yeah," he replies. "I don't know of any music that is more erotic than this. Alongside Tristan, Richard Strauss is like soap, just not honest."
Do Wagner's famously slippery harmonies have anything to do with this sensation? Another smile breaks out as Stier describes this music as "an ecstasy and tension that are never relieved. The cadences don't close off, and it just goes on and on".
The first meeting of the lovers is an example.
"Tristan and Isolde meet and have sex, leading up to the first big orchestral climax," he points out. "Then they lie down and start up a new conversation, which takes 10 to 15 minutes in real time. By the end of this, familiar feelings are stirring up again."
Yet despite Tristan and Isolde being legendary lovers on a par with Dante and Beatrice or Romeo and Juliet, "Wagner portrays them vividly as human beings", Stier counters.
"Their first meeting, or perhaps we should call it their first date, is like a big argument," he laughs. "When Act III opens, there is this pervading emptiness after all that fantastic sex and love. And through it all Wagner's music is reacting, interacting and driving it along."
Stier is thrilled that Auckland will be experiencing some top international singers next Saturday, headed by Swedish soprano Annalena Persson, who sang the role in Seattle four years ago. One of her challenges is to catch a character "at once demanding and disruptive. Isolde shows devotion at the end, but along the way her passion is sometimes ruthless".
Stier is delighted that Tristan will be played by Swedish tenor Lars Cleveman, a seasoned Wagnerian on the stages of Covent Garden, the Met and Bayreuth.
Tristan as a character might be "a bastard and a killer", Stier explains, but Cleveman's voice is "so strong with a golden tone that I think you'll like".
Danish baritone Bo Skovhus, taking the role of Tristan's friend Kurwenal, is "a big star in Europe", playing the character of "a brave heart who is sometimes a little bit stupid but always trying his best. I think we're in for an inspiring performance", Stier nods. It is difficult to select highlights from Wagner's vast four-and-a-half-hour musical panorama, but Stier settles on the Prelude, which is "like the opening of a big new movie", as well as alerting me to echoes of Weber in Act II's nature music.
Yet in the middle of all the complexities that we associate with Tristan und Isolde, Stier settles on the final aria from King Marke, to be sung by Danish bass Runi Brattaberg. His grief for the dead Tristan is "so touching because it's so simple".
Consumed by love
Wagner's Tristan und Isolde changed the course of musical history with the very first chord of its Prelude. This highly ambiguous harmony would inevitably lead to the break-up of music as the 19th century knew it.
Introducing the opera to a gramophone audience in the late 1920s, English writer Alec Robertson caught the power of Wagner's opening phrase in more colloquial terms. Once those few notes had been heard, he claimed, "the listener is now no longer Mr Jones or Mrs Brown. He is Tristan, she Isolde".
More recently, the same music was a potent force in the soundtrack to Lars von Trier's 2011 film, Melancholia.
Tristan und Isolde was premiered in Munich in the summer of 1859, under the sponsorship of the eccentric King Ludwig of castle-building notoriety.
Its tale of two ill-fated Celtic lovers was a paean to love; in the words of its composer, "a monument to the loveliest of all dreams".
The basic premise is simple, but deeper issues resonate beneath. The young Tristan is deputised by his uncle, King Marke, to fetch the monarch's bride-to-be, Isolde.
Spurred on by an inadvertent love potion, Tristan and Isolde are consumed with passion for one another in their great Act II love duet.
The outcome is predictably tragic. Tristan is slain and Isolde takes her own life, but not until she sings her transcendental Liebestod, with its very Wagnerian melding of love and death.
Tristan und Isolde has all the hallmarks of Wagner's style. An intricate network of themes or leitmotifs underpins the singers' contributions, down to the use of certain instruments for various characters and emotions.
The eroticism of this music is palpable. Clara Schumann was disgusted by it and, as late as 1957, the American author Carl Van Vechten wrote to the young novelist James Purdy that Wagner's Prelude was an accurate description of a sexual act, using the racier Anglo-Saxon terminology.
However, the ultimate victories of Tristan und Isolde are musical ones, caught by Debussy, who was bowled over by the subtlety and integrity of its orchestral component. Here there was "constant equilibrium between musical necessity and the thematic evolutions".
The triumph of this opera is one shared by singers and orchestra, making it an ideal choice for a concert hall presentation.
What: Tristan und Isolde, with the Auckland Philharmonia Orchestra
Where and when: Auckland Town Hall, July 19 at 4pm
