The following news may be greeted with rejoicing or horror: The Tallis Scholars, the British chamber choir that made an international reputation based on music written before 1600, has been joining the 21st century - and brought its updated self to the Cathedral Basilica of SS. Peter and Paul on Friday.

The beloved Estonian mystic minimalist Arvo Pärt, now 80, dominated the program, but was heard alongside music of the group's 16th-century namesake Thomas Tallis and his near-contemporary John Sheppard. The pairing wasn't as easy as it looked. Often, Pärt's ascetic, pared-down choral music is a sketch of a larger, more profound experience; the 16th-century masters were often out to create magnificence in totality. The earlier composers also tend to conclude with resounding resolution; Pärt often ends with questions.

Tallis Scholars director Peter Phillips carefully chose Sheppard's Sacris Solemniis with its straightforward utterance interspersed with monophonic hymns, as a bridge from Pärt's spare language to Tallis' dense Missa Puer Natus. So there was no sense of a forced marriage. The famous Scholars sound was particularly evident in Sheppard's Gaude, Gaude, Gaude, celebrating the Virgin Mary at Christ's birth.

The Pärt portions had deceptive challenge: As much as the composer's works often sound alike superficially, they wrestle with all manner of compositional problems. One never knows how Pärt will pair words and sound. At times, words seem to be along for the ride in the grand design that is his Magnificat, which rises to raging fortissimos. But in the brief Seven Antiphons, Pärt uses a different sound world for each of the brief texts. In I am the True Vine, words have childlike delivery with framing devices that include long-held soprano notes or growling, elemental bass notes.

How the Tallis Scholars figured into the pieces sung in Friday's concert was blessedly predictable. The trademark vocal sheen gave Pärt's often-simple vocal lines a welcome luster while also clearly delineating the piece's intermingling elements, spelling out with particular clarity what is (or is not) happening in the piece. The 10-voice group lacked the vocal magnitude to go to the edges that the music sometimes explores; the underlying intensity needed to sustain Pärt's simplicity wasn't much in evidence. The Tallis Scholars' commitment to seamless vocal beauty doesn't fully accommodate Pärt's delving into the mysteries of existence in the anguish of modern times. But then, how often does Philadelphia enjoy such a provocative program?