There are two CDs by the Clerk's Group including the de la Rue Requiem. This one also includes the Brumel Requiem, its first recording, and it's a bold exciting piece of polyphony. There is also a CD of the de la Rue Requiem by Ensemble Officium. IMHO The Clerks' Group performance is easily superior, and I've found that most listeners, hearing the two blind, agree. Officium produces a huge, resonant, glorious choral timbre (perhaps with a little studio resonance added) but at the cost of a "generalized" quality both of tuning and of expression. The Clerks' Group coaxes as much emotional intensity out of the standard Latin text of the requiem mass as anyone could hope. See my other review, of the Ensemble Officium disc, for more detail.