The Sacred Music Colloquium featured a huge range of music for Mass. One Mass was set aside for the women's choir of St. John Cantius to prepare so that the colloquium choirs could have a break. I'm linking here my favorite piece from their Mass ordinary. It is a Gloria from the Mass in E-Flat, Op. 15, by Josef Rheinberger (1839-1901).
From my reading of 19th and early 20th century Catholic classics, this piece might have been a choir pick for a cathedral in preconciliar days. I like it very much, despite the slight hints that date it a bit (dated in a way that, e.g. Josquin or Victoria or Byrd are not).
Rheinberger was not of the sentimental Caecilian school and, in fact, was a critic of self-conscious anachronism in liturgical music. He was a serious guy, and his music always made the "white list," and for good reason. It is not what I would put at the top of the list of the "treasury" but it is worthy music and it is a great thing that Cantius is preserving its use in a liturgical setting.