The choirs of the Anglican Church of St James, King Steet, and the RC Cathedral of St Mary, are this Sunday (14 August) at 5 pm o'clock to sing the First Vespers for the Assumption of the BVM at the aforementioned cathedral. The men of the Cathedral Choir (and for the major feasts, as would appear to be the case in this instance, the Full Choir) sing Solemn Choral Vespers & Benediction at 5 pm almost every Sunday, with the whole service being in Latin except for the Scripture Reading, the intercessions and the Lord's Prayer.
The order of service has not been released, but as the Vespers is part of the Sydney Victoria Festival, celebrating the 400th anniversary of that composer's death, it is a fair bet that his music will pervade the service.