Arnold Schoenberg married two different women, each of whom had a brother who was a well respected musician in Vienna. His first wife, Mathilde, was the sister of composer Alexander von Zemlinsky. His second wife, Gertrude, was the sibling of violinist Rudolf Kolisch, whose string quartet premiered works by Schoenberg.At his Society for Private Musical Performances, where Kolisch was a prominent member, Schoenberg promoted the music of Béla Bartók, even inviting the Hungarian to Vienna to present his new music.

In 1941, after Schoenberg, Kolisch, and Bartók had fled to New York, Kolisch’s quartet performed the world premiere of the last piece written by Bartók before leaving Hungary, the String Quartet No.6,which many consider the finest since Beethoven. Sunday at the Walter Reade Theater, the Leipzig String Quartet featured this as part of the Mostly Mozart Festival series.

The group’s members (Andreas Seidel and Tilman Buening, violins; Ivo Bauer, viola, and Matthias Moosdorf, cello) have a solid reputation and an impressive discography as modern music specialists. Three of the four men are former first chair players of the Gewandhaus Orchestra.Their performance, from a technical point of view, was stunning, especially the finely wrought balances, sharp enunciations, dexterous interplay of melodic material, and arrestingly eloquent sotto voce. My only displeasure arose from the group’s rather cold, empirical distillations of the normally affecting emotional content of the composer’s last words on the subject of quartet writing.

Bartók was fascinated by musical architecture and fashioned a new blueprint for this piece, preceding each movement with a naked theme, marked “mesto” — with sadness — in the score. Although Mr. Bauer — who, a propos of nothing in particular, is the doppelganger of Anton Webern, complete with similar eyeglasses — intoned the first iteration with sensitive vibrato, the three following renditions, one featuring the cello and one the first violin, were less in touch with Bartók’s shattering worldweariness. This version displayed moments of great power — for example, the soaring violin melody played over a guitarlike strumming of the viola in the Marcia, or the suggestion of the barbaric in the Burletta — but too much of the time the quartet seemed intent on an emotionless deconstruction of the piece. Every note was perfect, every transition seamless, every hair in place. This realization reminded me of that famous comment by Budapest Quartet violist Boris Kroyt that it was indeed possible to practice too much.

It could be argued — although not by me — that Bartók was in a nihilistic mood when he composed his final quartet, which would render this Leipzig forensic approach somewhat appropriate.But to turn the same scalpels on early Beethoven just seemed wrongheaded. If the Bartók Sixth is the omega, then the Beethoven Sixth is the alpha, one of a half dozen quartets written at the same time inaugurating that greatest of all compendia of chamber music with a rollicking start. Any of these early quartets should be highly enjoyable in live performance, but this one seemed constrained, forced, kidnapped. Judging by the polite but lukewarm ovation from the Walter Reade audience, the crowd was hardly swept away.

This was a pity, as the quartet exhibited some of the best string playing I have heard in quite a while.Very sensitive to dynamic changes, these four experts established a peaceful quietude that might have allowed the thematic material to breathe had they not kept it so closely under wraps.Stereotypes tend to have their genesis in fact and there is no question that this was a German aesthetic at work: the triumph of precision mechanics. As a result, individual passages could be breathtakingly lovely — for example, the last measures of the Scherzo, which featured extremely delicate conversation between first and second violins. But missing was what the late Jupiter Symphony conductor Jens Nygaard used to call “Beethoven’s muddy boots.” Although not as raucous as the later symphonies, the early quartets depended on a sense of the country dance and a slightly uncoordinated peasant rhythm. Beethoven could still hear when he composed the Quartet No. 6 and anecdotal evidence seems to indicate that the performances he would have experienced were nowhere near as technically accurate as this one, but I daresay that they were a lot more spirited.

Mostly Mozart Festival through August 26 (Lincoln Center, 212-721-6500).