Finding settings that amplify an opera’s drama has long been Mr. Einhorn’s mission. Since 2012, On Site Opera, which he helped found, has put on productions in unusual spaces, including the Bronx Zoo (Shostakovich’s “The Tale of the Silly Baby Mouse”), a church crypt (Gregg Kallor’s “The Tell-Tale Heart”) and Madame Tussauds (Rameau’s “Pygmalion”). But in telling the story of the crippled shepherd boy Amahl and his life-changing encounter with the three kings drawn by the star of Bethlehem, Mr. Einhorn decided to find not only the right place, but also the right people.

Speaking of the backgrounds of his amateur choristers, who will share the stage with professional musicians, Mr. Einhorn said he had taken care “to be sensitive to who these people are and never to go into an exploitative territory in how we talk about them, or how we fold their experiences into the production itself.”

Printed programs will reflect some of the biographies of the singers. But even without these, audience members may pick up, here and there, on the signs of past deprivation that appear etched into faces. The four years she spent on the streets of New York have certainly left their trace on Laura O’Day, 57, whose lined features broke into a smile as she spoke about her participation in the opera in an interview.