That, plus the expense of printing and renting the thick scores, partly explains why the piece fell off the map, said Hayes, whose performance two years ago in Philadelphia was only the sixth complete one, the last having been 30 years prior. So far does the piece stray from the typical requiem that even the most sophisticated observers are apt to come away from it wondering, "What, exactly, is it?"
In place of the usual liturgical text, the composer assembled more than 50 Scripture quotations in a double choral format: One side represents the aggrieved living, the other the departed souls in paradise. Spirited interaction - what Hayes describes as "choirs interacting in completely different spheres" - unfolds without the benefit of instrumental accompaniment.
The first full performance at Harvard University had such badly sagging pitch that one critic compared the effect to "the weird impression of a record being played one speed too slowly."
What prompted the composer to depart so dramatically from the college choir pieces he typically wrote? Perhaps his head was 400 years in the past.
"One thing in the back of his mind was the Renaissance-era madrigal cycles," said Zachary Vreeman, director of choral activities at Casper (Wyo.) College, whose dissertation was on the Thompson Requiem, "though I've never come across something so heavily dramatized in a choral work."
At times, the choruses seem to be shouting at each other.
No doubt, the composer was wrestling with mortality issues as never before. The Requiem was begun in 1954 - the year one of Thompson's closest colleagues, conductor Stephen Tuttle, dropped dead. Though biographical sources say Tuttle died at home, he, in fact, expired in Thompson's driveway in Cambridge, said Carl Schmidt, a Thompson student and family friend, now a music history professor at Towson University.
The same year, Thompson got to know promising young choral conductor Frederick S. Pratt II, who was told he had months to live and longed to give something back to the art form he loved. Ideas they had discussed were going into his forthcoming piece, Thompson assured him - in a letter that arrived the day after Pratt died.
The Requiem drew conceptually from Pratt and stylistically from Tuttle, one of the early experts in the Renaissance choral music that Thompson seemed to draw on. The wide-ranging scriptural references were possible because Thompson (a churchgoer, though not a Bible pounder) attended prep school at Lawrenceville, N.J., where religion courses were required.
"He learned the Bible well and wrote down on note cards his favorite passages," Schmidt said.
Further back in his mind, Thompson was perhaps drawing on Thornton Wilder's 1938 play Our Town, whose third act has the dead and the living mingling on stage.
"He didn't start out writing for a performance. It was the first piece, maybe the only piece, he started without a commission," Hayes said. "It's as if he poured everything he knew about writing for a cappella mixed choir into one work. Sometimes the extravagances of it are really astonishing."
Only later did the University of Southern California come through with a carte blanche invitation to commemorate the opening of a new hall. At the premiere, however, piano accompaniment was needed to bolster the vocal forces.
By the time Hayes stumbled upon the score at a Cambridge music store, the piece was available in an alternative version with string orchestra accompaniment. But the price tag for the hefty score was too much for his teenage budget. Only later did he reencounter it while sifting through scores left to the Philadelphia Singers by its founder, the late Michael Korn, who shared with Thompson a Curtis Institute connection. (Korn had graduated from there; Thompson ran the place in 1941 and '42.)
"The more I worked on it," Hayes said, "the more I thought we should really do it."
The March 2012 performance was extremely well received, but Hayes knew there was much further to go.
"The big achievement is that we got the piece to work," he said. "Coming back to it, there's a sense of starting from a place where it already feels right. A lot of composers have trouble writing expressively in English. Thompson set texts that communicate immediately."
Fund-raising for a reprise performance - and a much-needed recording to follow - was tough. Thompson's "Alleluia," written in 1940 for the opening of the Berkshire Music Center, sold three million copies of sheet music. But one failed endeavor on the fund-raising platform Kickstarter brought in only 5 percent of the $19,500 goal. Ultimately, the Presser Foundation came through. But since Thompson's 1984 death at age 85, his reputation has been in eclipse.
"It's not an unknown name or a scary name," Hayes said, "but it's not a sexy name."
Those trying to change that are scattered around the country, but they're there. "I'm doing my best," Schmidt said. "I have in front of me the proofs to my 500-page catalog of his works." Next is a full biography.
Even if the Hayes recording is a significant success, the Requiem still could have traction problems because it can't be taken piecemeal: Individual movements can't really be performed out of context. "They don't make a lot of sense out," Vreeman said.
With its grand design and highly personal inner impetus, will the Requiem ever sit comfortably anywhere?