Mass XVII with Kyrie C is nice, and it's quite easy to pick up. I think you'd be safe, there.

I'd also like to know more about why certain Ordinaries are associated with certain seasons. My guess is that the classifications are more conventional than principled, but that's just a guess.

It's tempting to register some impressions: I Lux et Origo is "fresh" sounding, spring-like, with all its major thirds; IV Cunctipotens genitor Deus is dark and mysterious; VIII is cheerful and melodic; XVIII is so barren and spare; etc.

I've never understood why Mass IX - Cum iubilo - is "jubilant." Maybe it's on account of its Sanctus and Agnus Dei. The Kyrie certainly sounds penitential with its descending lines and minor thirds. The Gloria is really superb.

I'd go with IX before Orbis Factor (XI). I've always thought the latter sounded more like Lent.

In our church we sing "De Angelis" usually. But for Advent and Lent we use "Orbis Factor".
We cannot change more often because ordinary is sung by all (not only by our schola - they are concerned with propers).
It would be difficult to teach the congregation more Masses now.

The more familiar Kyrie is C under Mass XVII (in the Gregorian Missal and the Graduale Romanum 1974; ad libitum in the Liber Usualis). A small group of us sang for a weekly Latin Mass with a somewhat inexperienced congregation. They knew the Missa de Angelis well and sang it year round. Then we introduced Mass XVII (with Kyrie C) on the Sundays of Advent and Lent—that gave ten Sundays of the year to absorb the new ordinary. By Lent, they were singing it moderately well, and by the end of Lent, almost as well as the de Angelis. The next year we introduced Mass I for the Sundays after Easter; that took a bit more time, but eventually it was sung well also.

I would not use Mass XVIII for the very reason that it does belong to weekday Masses and Requiems—the occasion for the most sparse music of the year. The Sundays of Advent and Lent, while penitential, are still Sundays and bear some solemnity. Mass XVII really does convey that, while being quite distinct from those of the rest of the year.

An alternative is Mass XI (Orbis Factor). The Kyrie is a real classic (see my article in Sacred Music, 133:1). If you are using de Angelis on the Sundays of the year, Mass XI would provide the contrast and the solemnity for Advent and Lent. Still, even better would be to alternate de Angelis and Orbis Factor during the Sundays of the year and use XVII for Advent and Lent. It all depends upon the reception by the congregation. But that reception might be judged on a fairly long-term basis, over several years.

I'm grateful for this discussion. It gives me a better understanding of which Mass ordinaries would be appropriate.

On a related, but slightly off topic: My lay Carmelite group meets once a month, and the Carmelite monk who is our spiritual advisor, Fr. Donald Kinney, asked me and a man in the group to introduce more singing. The man in question is indifferent. He said something like, "Latin or not, it's all good."

On this topic, I remember hearing Prof. Mahrt explain the different levels of singing at Masses. When I asked about what to do at the Carmelite Mass, I recall that he told me that adding more music should start with the priest singing his parts. I haven't been able to broach the subject with the priest of his singing the priest parts, so I don't know whether that means that we as a congregation should not sing any Mass ordinaries until and unless the priest takes his part.

The only other clarification I have gotten from Fr. Donald is that he doesn't want our monthly Mass to become known as the "Latin" Mass. And he reminded me that I have to get the approval of the lay Carmelite council for what I do, which is indifferent to the notion of reintroducing chant.

The only clear mandate I have is to lead the Alleluia. Anyone have any suggestions about which one would work (sans the Gradual), which I am not up to leading, yet?

Would it break any rules to add the singing of the Our Father in Latin, if that was the only Latin I could introduce? I have a copy of Prof. Mahrt's version and it is very easy to learn.

When I joined, they already ended every Mass with the Salve Regina. I have added the novelty of leading Alma Redemptoris at our December Mass. And Regina Caeli for the Easter season.

Advice about where to go from her would be welcome.