"I think you need the lightness of Mozart in between the two darker works on Thursday - Schnittke's Concerto for Piano and Strings and Shostakovich's Twelfth Symphony."
But there was also another, more devious, prompting for Stier's programming.
"He knows I have a jazz cadenza for the third movement, written for me by Karsten Gundermann, and it's very funny."
The Schnittke Concerto dates from 1978. Alexander Ivashkin, the Russian composer's biographer, describes Schnittke as one of the busiest composers in the world at that time, working all day at film scores in the Mosfilm studios then returning home to fulfil a stream of concert commissions. I mention Ivashkin's theory that Schnittke considered the concerto a very symbolic form, with the relationship of soloist and orchestra echoing that of an individual standing up to the great majority.
Schirmer is interested, but not totally convinced. She sees this work as reflecting Schnittke's feelings of homelessness.
"It's there in all the musical influences that you hear coming out in the score, from Russian Orthodox chants to Viennese waltzes," she explains. "There are Russian parts, German parts and Austrian parts. There are also so many composing styles being used - 12-tone, bitonal and polytonal as well as the quite conservative - it's very intense."
Schirmer is always happy to work with Eckehard Stier. Their professional relationship and friendship dates from 2000, when she played Chopin with his orchestra. "From the first rehearsal we were d'accord," she laughs, slipping in a French word where some might have used the Italian term simpatico. "There's perhaps no such thing as a perfect conductor, but Eckehard gets very close. If you saw a video of him with no sound, you'd still be able to work out the music from his face and body, the way he moves. When he raises his arm, I know what to do."
When our conversation strays to more general musical issues, there are surprises. She collects vinyl records, of cherished pianists such as Wilhelm Backhaus, Sviatoslav Richter and Glenn Gould. With the eccentric Gould she loves his absolute concentration. "All that detailing in his recording of Bach's Well-Tempered Clavier. He didn't just stick to the rules, he did what be believed in, which is really something."
Schirmer chooses baroque music when I ask for favourites. "Bach is perfect in the way that he brings together vertical and horizontal lines ... Handel is so wonderfully alive. You're free to improvise and change things. His scores can be just a series of chords, a sketch for you to work with."
Evidence of Schirmer's flamboyant way with a Handel Prelude can be found on YouTube. Perhaps a sampling might turn up at encore time next Thursday.
What: Auckland Philharmonia Orchestra
Where and when: Auckland Town Hall, Thursday at 8pm