My understanding is that the two new Antiphonale Romanum volumes are to enable the chanting of LOTH Lauds and Vespers in Latin on Sundays and feast days / solemnities. The three Antiphonale Monasticum volumes (strangely bound in vinyl) are meant to set forth a monastic office according to Thesaurus Liturgiae Horarum Monasticae, although to use these volumes to actually chant a monastic office would involve a comical scene of book-juggling (a community would need to use these volumes as a resource to create their own usable office book). I thought the Liber Hymnarius was supposed to give the chants for hymns in the Latin LOTH, but I'll need to check.

Does anybody know of an English translation of the preface of the Liber Hymnarius?

Since I have the 2015 OCO, Les Heures Grégoriennes, the new Antiphonaire Monasticum (all available volumes), Liber Hymnarius, and both new volumes of the AR (I and II), plus the pre-conciliar Antiphonales Monasticum and Solesmenses, allow me to comment:

Les Heures Grégoriennes

My research shows that the ferial office of Ordinary Time follows the new OCO faithfully with one exception: for psalm 109(110), a different antiphon for each Sunday is used; Dixit Dominus is only used on Sunday III.

The main simplifications in LHG are: only one antiphon for the Gospel Canticle at I and II Vespers and Lauds of all Sundays; and for feasts and solemnities and weekdays other than OT, often repetition of the same Offices at Lauds and Vespers.

Without any proof, I suspect LHG (2008) came out during the thick of preparing the new OCO, and so is a bit "incomplete" in that regard except for the ferial office.

Antiphonale Romanum I and II

Brings everything that isn't in line with OCO in LHG, into line with OCO for Sundays, feasts and Solemnities. So different Antiphons at Lauds and Vespers; for the Gospel Canticles on Sundays, a different gospel canticle antiphon for I Vespers/Lauds and II Vespers. All feasts/solemnities are brought into line with OCO. As such I use a combination of LHG and OCO at least for Sundays, feasts and solemnities and just LHG for ordinary ferias and memorials; and sometimes when lazy, at other times; one advantage of rarely used but repeated antiphons, is that by II Vespers you start to get the hang of them! And I'm inclined to use Dixit Dominus for Ps. 109 every Sunday; after all I'm an oblate and that's what happens in monasteries. Also in AR I and II, *all* hymn strophes are noted (a blessing!), whereas in LHG often only the first strophe is noted, even on some fairly challenging hymns (feast of St. Lawrence at Lauds comes to mind).

Antiphonale Monasticum I, II, III and V (IV not released yet)

Yeah, a true pain in the derrière to use, and indeed our abbey used the books as references to publish its own choir books. There are a lot of common antiphons in both AM and AR. But differences too. Also, if you ask nicely, Solesmes will sell image files of AM I, II, and III making it easier to design your own books; one major flaw is the minor hours, as there are different schemas to dump the former psalms of Prime into the minor hours. They just throw out the psalms and corresponding antiphons, it's up to the community to arrange them according to the schema they use. Makes it almost impossible to use Volume II as a choir book for the minor hours. The old Psalterium Monasticum was more helpful in that regard, at least for the ferial office.

Liber Hymnarius

Indeed, all the hymns for the Liturgy of the Hours, plus monastic and Solesmes propers.

OCO 2015 sort of made life harder for guys like me who often prepare our own chant booklets to fill-in gaps where no books exist, for instance I made my own Nocturnale Romanum but based on the previous OCO. Most everything could be found in the Monastic sources, with a few exceptions from the Graduale Simplex, a couple of sources I found on line (1912 Antiphonale Romanum) and a couple of places where I borrowed from Sandhofe's Nocturnale Romanum, so rather non-official. But the sources in the 2015 edition are not always easy to find. So I'm sticking to my own Nocturnale for when I feel up to chanting the Office of Readings, which these days isn't all that often. I more often just read that Office after Compline before bed. Otherwise I combine it with Lauds into an office of Matins (at 6 am), as allowed by the rubrics of the LOTH; chanted, that's 40 minutes on weekdays, 45 on Sundays, Feasts and Solemnities thanks to the Te Deum.

Happy chanting!

Ora