In Kay's novel, Kevin Laine takes this song and uses it as the basis for "Rachel's Song"; the first verse of the song's lyrics are as follows:
Love, do you remember
My name? I was lost
In summer turned winter
Made bitter by frost.
And when June comes December
The heart pays the cost.
As far as I know, there isn't a version of the song that is exactly like what Kevin wrote, although artist and composer Martin Springett has recorded a version that, as Springett notes, makes "no attempt to paraphrase the Brahms cello concerto"--rather he "wanted [his] own emotions to enter into this." Springett has also recorded a whole album of music inspired by the works of Kay, which he talks about here.
Other composers and artists have been musically inspired by Kay's works as well--you can find a long list of them over at Bright Weavings, the authorized Guy Gavriel Kay fan site. One of these compositions is based on Kay's The Sarantine Mosaic, and was written by Canadian composer Paul Frehner and premiered in March 2010. Here is an excerpt from Frehner's program notes that describes what these books are about and how his music draws from them:
"The action in Kay's novels takes place in Sarantium, a fictional city and empire modeled after Byzantium in the time of Emperor Justinian, ca. sixth century AD. In the novels Kay vividly paints a sophisticated society that is both rich in culture and custom and filled with political intrigues and complex sub plots. Dichotomy of theological beliefs is a central line of inquiry. Though Sarantium is by imperial decree a monotheistic society, pagan superstitions and physical manifestations of the half-world are ever-present and hold sway over the lives of its inhabitants.
"Sarantine Polyphony consists of three movements. The music is not narrative in nature but is rather evocative of the imagery I received from place and character settings in the story. Melodically, I use at times an invented type of folkloric string writing that alludes in some ways to ancient Byzantine instrumental music.
Here is a recording of a performance of the second movement, entitled "Shirin's Dance." Shirin is the "daughter of an alchemist and the most celebrated exotic dancer in the city of Sarantium."
I'm quite impressed at how many composers and artists have created works based on Kay's work--not only does it speak to how strongly Kay's words influence others, but it also demonstrates how lyrical and musical Kay's words are to be so frequently translated into song.