Thank you. Let's hope that Continuum can issue some CDs of this repertory.

This all-male ensemble has made 16th century Spanish sacred polyphony and chant the core of its repertoire, and seeks to perform this wonderful music at the original, sonorous low pitch as it would have been heard in Spanish cathedrals and religious institutions during Spain's "Golden Age".

Excuse my ignorance, but please elaborate on this "original, sonorous low pitch". Were there reasons for that: musical, religious, national, or cultural?

A religious reason is that in this period of time women were not allowed to sing in church (the divine office and I suppose mass in nuns' convents excepted). Therefore the soprano and perhaps also the alto part had to be rendered by either boys (I'm not sure, whether this is the musically correct term, in German it would be Knabenstimmen) or falsettists (spanish falsettist are credited to have sung in the Vatican in the 16th c.) or castrates (which had the beginning of their great time after this period). Therefore it would not be wrong to render the pieces lower (and give the bass part to bassi profondi).

The pitch standard Adam mentions is not universal: I often have the opportunity to play on a 18th c. organ in so called high cornet pitch with a' = 467 Hz or so; for Italy there is evidence for a high pitch in the Lombardy, a low pitch in Rome and a middle pitch in Venice.
In those times several pitches were differentiated, chamber pitch (Kammerton, ca. 392--415 Hz) for chamber and orchestra music, choir pitch (Chorton) usually to a major second lower than chamber pitch, and cornet pitch up to a terce higher than chamber pitch.

I wonder what factors came into play for the placement of voice parts/singers and microphones, as I heard one CT soprano predominantly, and at a fairly consistent mf volume without much contour. Could, of course, be the limitations of the playback via YouTube delivery, etc. Was the gentleman bass far stage right one of the directors? He had an interesting jaw placement, looked a little tense, but the tone was resoundingly solid! Kudos.

Adam ... you're alright whether you're all right or half-right!

Actually "Old Philharmonic" pitch lasted until the move to A440 in the 1930s in the brass bands of England. You can still get instruments (lots of them) on Ebay at that pitch.

Michael, you are absolutely right. At low pitch with an adult-male choir, each voice is in the most exciting part of its range, which isn't the case with editons of sacred polyphony transposed upwards and sung by modern SATB choirs (the alto part especially being too low and often inaudible). There's lots of research on this which was done 30 years ago by Bruno Turner, Continuum's musicological advisor. Archival research shows that Spanish choirs of this time consisisted of adult male voices: "Tiple" or soprano (adult male high falsettists), alto, tenor and bass. Boys in Spanish cathedrals and religious institutions normally sang only plainsong, which gave them an incomparable musical training, with the polyphony left to the adult, experienced, singers. Bruno Turner's group, Pro Cantione Antiqua, in the 1970's and 80's, recorded much continental sacred polyphony from the 16th century using the original pitch. As I understand it, the upward transposition is a relatively recent phenomenon, started in the 19th century to make earlier music singable by modern SATB choirs, and then in Oxford in the 1970's and 80's, Peter Phillips and Harry Christophers formed ensembles and began recording music at transposed pitch, and now it's seen as the norm, when it's really quite a recent invention. Choirs singing at high pitch can sound glorious, of course, but it's entirely different in character from the original. I should add that the subject of performing pitch in early English music is more complicated and isn't resolved to quite the same degree as continental music.

Pitch standards were worse than what you might think:

Concert "A" pitch since 1511

A=403 (Mersenne spinet, 1648) to A=561 (Praetorius "church pitch", 1619), and nearly everything in between.

The instrumental "baroque pitch" at about 415 was anywhere from a major second to a minor third below the Chorton pitch of singers, and transposition was often required.

Indeed, Michael. A=415 also conveniently corresponds to a semitone lower than A=440, so that by transposing downward a semitone, modern instruments may be employed alongside baroque instruments. There are harpsichords made with a mechanical provision for such downward transposition - the manuals shift to the left to accomplish this - when it is desired to perform at A=415. The whole issue of performance pitch is fascinating - and sometimes frustrating!