The Op. 104 Fünf Gesänge are something else again — denser, bleaker, more concentrated in expression, rather like choral analogues to the late piano music. Late Brahms is perennially and irritatingly labeled “autumnal,” but here the theme is quite literally autumn: dead leaves, fading sun, falling darkness, lost youth, approaching death. The bittersweet, deeply fraught emotional tone of the songs was caught with great specificity. The sheer physical vitality of remembered youth in “Verlorne Jugend” (Lost youth), for example, shone through the resignation of music and text, while the great concluding paragraphs of “Im Herbst” (In autumn) were serene and deeply sorrowful at once.

Two part-songs apiece fell to the male and female contingents of the choir. For the 16 men it was Schubert: Die Nacht (The night), D. 983c, and Lied im Freien (Song in the outdoors), D. 572. Taken together, these pose two quite different sets of technical challenges. Die Nacht is a tiny piece in chromatically inflected close harmony, extremely simple in concept — a sort of ethereal barbershop quartet. The choir balanced it perfectly and sang it in exquisite pianissimo. But the real marvel was how the first tenors managed the leap to the high A toward the end of the tune: smoothly up and back down with no sense of a hiccup in the line or uncertainty about the pitch. It was magnificently done, and when the last time through the note has a fermata on it, the effect was magical.

Lied im Freien, by contrast, begins in a naive, hearty vein suggestive of a band of sturdy Germanic folk lustily singing as they hike. But the bluff simplicity is Schubert's tease, for the piece proceeds to go through a tortuous series of sudden modulations, extreme even for Schubert at his most harmonically adventurous. If this is a hike, it’s one through uncommonly treacherous terrain. But the RIAS men never put a foot wrong; the exultant ring of triumph in their voices, when at length they found their way back to the tonic, felt thoroughly earned.

The 20 women, for their part, had somewhat less demanding assignments in the shape of two Schumann part-songs: In Meeres mitten (In the middle of the ocean), Op. 91/6, and Meerfey (The mermaid), Op. 69/5. Both are lightly fanciful music, the first culminating in a touching maggiore third stanza that the women sang with melting beauty of tone.

If the Brahms, Schubert, and Schumann showcased a marvelously assured and robustly full-voiced ensemble, it fell to the rest of the program to illustrate, in more graphic terms, the extent of the choir’s technical accomplishment. First came two Mahler songs, in a cappella arrangements by one Clytus Gottwald. Transcribing Ich bin der Welt abhanden gekommen (I am lost to the world), Mahler’s glorious Rückert setting, for choir is perhaps an idea that might better have remained unrealized. The appeal to Gottwald is obvious from what he did with the song: Since the whole of Mahler’s delicate orchestration lies within the range of one or another human voice, why not just text every line and sing them all at pitch?

It works, in the sense that all the notes are there, but it makes something of a hash of the musical logic. The lines that inevitably stand out aren’t always the ones that should. Furthermore, while a choir as strong as this one can sing everything, a lot of the arrangement can’t help but sound strenuous. It’s nice to know that there are sopranos who can sing, for example, the line going up to high D that Mahler gave to a solo violin, but on a violin it is easy and comfortable, while when sung (no matter how well), it is, obviously, dauntingly high. The performance was all it could be, but still not enough to convince. “Die zwei blauen Augen” (The two blue eyes), the last of the Lieder eines fahrenden Gesellen, on the other hand, worked much better in Gottwaldized form, largely because here the melodic line tends to stay on top of the texture, rather than being enveloped in it.

Ending with a group of pieces by György Ligeti certainly suggested an outsize level of self-confidence, which proved amply justified. The set began with a pair of early (1955) Hungarian-language works for eight-part choir: Éjszaka (Night) and Reggel (Morning). The first is a piece of striking and uncanny effect. The voices fan out gradually from an initial unison to a prism of pitches, opening ever outward and upward, gaining intensity over an incessantly repeated rhythm. Suddenly it is all whisked away, and in its place is a stark senza vibrato, pianissimo chord of sharply contrasting harmony. The companion piece is a jolly riot of morning sounds, cock-crows and alarm clocks featuring prominently. Both pieces are extremely brief, vivid, exacting, exhilarating.

Drei Phantasien nach Friedrich Hölderlin, from 1982, is much denser and gnarlier stuff. The voices are in 16 parts here, often in close canon rhythmically and in compressed clusters harmonically. The effect is sometimes of an impenetrable, solid band of vocal sound, sometimes of a teeming texture that seems on the verge of achieving a kind of spontaneous regularity, but dissolves back again into mist. There are dynamic extremes, too: extraordinary chords hit with a force that seemed doubly overwhelming Thursday because of the palpably dead-on accuracy of the tuning.

The volume was almost physically intimidating. It seemed impossible that so much sound could come out of such a small group of people and yet not sound in the least like shouting. Equally impressive were the quietest moments, which deliberately skirted the threshold of audibility. It was not always easy to understand what was going on — indeed, the text is much of the time more raw phonetic material than bearer of meaning — but it was always utterly fascinating to the ear.

The choir was understandably reluctant to follow that tour de force with any sort of encore, but around the fourth curtain call — this one compounded by much rhythmic banging of feet from part of the audience — Wood and his singers acquiesced with a glowing rendition of Joseph Rheinberger's Abendlied (Evening song), Op. 69/3.