The star soprano Renée Fleming, who has been sheltering in place at her home in Virginia, recalled that when she heard from Mr. Gelb, she told him, “Well, nobody can say they’re busy.” Joking aside, she said, she agreed to take part because she wants to help the Met and other organizations “maintain a connection to their audience.” (She also has some experience with homespun performance, having recently made a video of Schubert’s “Ave Maria” remotely with the pianist Evgeny Kissin.)

All the artists participating in the gala are donating their time. “It’s totally a labor of love and, I think, an opportunity for people to do something,” Mr. Gelb said.

With seven-figure financial support from the philanthropist Mercedes T. Bass and Rolex, the Met has pulled together an enterprise for less than $100,000 that blends the lo-fi quality of Skype and the broadcasting might of the company’s Live in HD series. Some parts will be prerecorded: Mr. Nézet-Séguin, not using a click track but, rather, a video of his conducting — which, he said, will be “more human and warm” — has already led members of the Met Orchestra in excerpts from “Lohengrin” and “Cavalleria Rusticana,” and choristers in “Va, pensiero,” a crowd favorite from Verdi’s “Nabucco.”

The live portions will be powered by four channels, two of which will be needed for the stream’s technical back end. That leaves one for whoever is on camera, and one for the singer on deck — so none of the performers will be seen or heard until shortly before their moment in the spotlight.

Mr. Gelb’s week, then, has been filled with tests: half-hour Skype calls with singers and technicians including Gary Halvorson, the longtime Live in HD director. Through trial and error, they have sought sweet spots of Wi-Fi signals and sound balance; Mr. Mattei eventually found his light not in his living room, or in his boathouse, but in a nearby studio where he learned the title role of “Wozzeck” for the Met.

Even well-prepared singers have run into difficulties. The soprano Angel Blue — who will perform from her basement in New Jersey, in front of a framed photo of the Met’s old theater — had marking tape and good lighting. But her phone’s mic was unreliable, producing a tinny sound, so she was asked to change devices and return for another test.