After the orchestra gave a spirited reading of Mozart’s Overture to Così fan tutte, Ax bounced onto the stage. In an excited but avuncular manner, he introduced the audience to the 1805 Johann Fritz fortepiano on which he would play the Concerto No. 17 in G Major, K. 453.

I have no preference in the "historically informed" vs. "modern performance" divide. But matching an early piano with a modern orchestra, even a sensitive and chamber-sized one, is a little like seating Holden Caulfield next to Auntie Mame. It wasn’t so much a question of volume; I was seated in the sixth row and still couldn’t hear a couple of things. The real mismatch was the brilliant, incisive tone of Orpheus’ strings, which swamped the piano and reversed the normal focus of a concerto. If it hadn’t been for Ax’s irrepressible pianism, the whole enterprise might have crashed and burned.

As it was, the partners were so attuned to each other that you mainly noticed the finely coordinated byplay between soloist and orchestra, especially the winds, all of which is so crucial in Mozart’s concertos. One example of many: In the first movement, after the piano introduces its own elegant, short-phrased theme in D major, the winds echo it with a one-measure cadence figure, puckishly counterpointed by the piano. But then they set off unexpectedly into D minor and some far-out harmonies, outlined by the winds. Then, as if to say, “Enough,” the piano pulls out a cadence figure from earlier in the movement and hands it off smoothly to the winds, who prepare the entrance of the piano with the next theme. By observing the staccato, short phrasing on either side of the harmonic digression and by matching each other’s soft, legato tone within it, Ax and Orpheus’ wind players brought a lovely moment of shade into a sunlit garden.

The piano, early or modern, functioned as an extension of Ax’s personality in these performances. He never addressed the piano as if seeking to bring something out of it, but instead acted loosely, almost carelessly. He swept his hands over the keys, bringing out interior lines and harmonies in, for example, the long modulatory passage of the second movement. He often craned his neck toward the wind section, seemingly disconnected from what his hands were doing. This is self-effacing mastery of a special kind, and the effect was to draw attention to the music-making, and away from the soloist.

Ax’s supreme dynamic control and sensitivity tended to make even the most spectacular passagework sound easy. Even the zippy third movement, propelled by 16th-note triplets, was dispatched with simplicity and grace. As the main theme of the sonata-rondo came around, Ax eased up on the throttle, attenuated the volume, and made the theme’s entry totally natural and lucid. There was no visible effort, just Mozart’s music.

By contrast, the “Haffner” Symphony lives on the edge. It’s all about souped-up, edge-of-your-seat brilliance. Orpheus, with a particularly demonstrative violinist in the first chair, charged through the piece with all the energy you could wish for, from the opening octaves and "Mannheim rockets" (rapid, upward-moving scales), to the coruscating passagework in the finale. As in the concertos, winds tended to be featured in the orchestral balance, instead of discreetly folded into the texture. It was a stylish, dashing performance that confirmed, once again, the orchestra’s reputation for peerless ensemble playing.