Well, there are certainly a lots of works the Swingle Singers have
done that I'd love to get copies of.  Unfortunately, nothing I've found
indicates that they were the bunch who did the Adagio.  (It doesn't mean
they didn't, of course, just that the discographies I've seen don't list
it.)

Thanks for the help, though, everyone - I'm sure I'll find it eventually!!

Marguerite