The opera, brought to the screen in 2005 and based on the 1997 short story of the same name by Annie Proulx, opens on January 28 at the Teatro Real in the Spanish capital, some six years after it was commissioned.
"The whole opera is about a typical kind of impossible situation, a tragic situation," said the opera's 75-year-old American composer, Charles Wuorinen, who was supervising rehearsals in Madrid this week.
"In this case, it is two people who in some way want to have a relationship, which in their time is forbidden by society," he told AFP in an interview.
Wuorinen said he worked closely with Proulx, whose original short story was published in The New Yorker before being transported to the screen by Taiwanese director Ang Lee.
Depicting the tormented love story of two young cowboys, Jack and Ennis, who meet in the spectacular yet hostile mountainous region in Wyoming, won three Oscars.
"The importance of Annie Proulx's novel is that great love is great love even if social reflections and conventions are opposed to it," said the Teatro Real's departing director, the Belgian Gerard Mortier, who commissioned the adaption to opera in 2008 from the American composer and Proulx.
Mortier said he deliberately scheduled "Brokeback Mountain" to open straight after the performances of Wagner's opera of the adulterous love tragedy, "Tristan und Isolde".
"Tristan, Isolde, Jack, Ennis; they all don't understand what's happening to them but are all prepared to die for the love they feel," Mortier said in a statement.
The author of more than 260 orchestral, choral, piano and percussion compositions, as well as of electronic music and ballets, Wuorinen, a New Yorker, denies creating "Brokeback Mountain", in which the two heros kiss on stage, as a message in favour of homosexual rights.
"If that helps, that's good. But I'm more interested in the fundamental human problem because I would not want the opera to be thought as an ideological or propaganda piece for a particular point of view," he said.
Composed in two acts over two hours, with dialogues in simple English with some swearing, "Brokeback Mountain" is scheduled to run at the Teatro Real until February 11.