The tenor enjoys being in the middle of it all. "It takes me back to my brass band days, playing tuba, surrounded by that immense sound. Wagner loves the brass and we used to play Lohengrin, Tannhauser and Gotterdammerung as well as standard brass band music."
An elderly Rossini once said Wagner had beautiful moments and bad quarter-hours but O'Neill does not understand those who are frightened by the German composer's expansive time-frames. "Some might feel the same about going to those films of the Tolkien books," he counters. "But once you've been bitten by the Wagner bug there's no getting rid of it."
There is a break in our conversation while O'Neill organises lunch for the builders at his North Shore home, with meat pies and cream buns complemented by vegetarian sushi.
Pies, alas, are verboten for him as the stamina required for Wagner demands you are "healthy in both voice and body".
The key to it all is energy, he says. "I can't stand anyone who's not energised on stage, regardless of their physique. I call them oxygen-stealers. Audiences want to feel energy and passion invested in the music and, on Friday, there's certainly going to be that."
Behind O'Neill and Goerke, the NZSO will "play the hell out of Wagner's music," he says, thanks to the baton of music director Pietari Inkinen. "Pietari's a great singers' conductor," he adds. "As with Barenboim and Levine, there's never just one speed or one way of doing things.
"There are many ways, and he moulds the orchestra into the individual tone of each singer. That's a great conductor."
Performance
What: Wagner Gala with the New Zealand Symphony Orchestra
Where and when: Auckland Town Hall, Friday at 7pm