Inna Faliks (Lisa Marie Mazzucco)

Sunday’s concert at the National Gallery of Art posed an existential question: Is Mahler really Mahler without the cowbell?

For the Austrian composer, the rustic ring of the cowbell took on profound significance in his symphonies, representing cosmic solitude in the face of eternity. Pianists Inna Faliks and Daniel Schlosberg put that proposition to the test, doing away with the cowbell — and every other orchestral instrument — in a herculean performance of Mahler’s Sixth Symphony arranged for piano.

This four-hands version, arranged by Alexander Zemlinsky, comes from an age when amateurs relied on piano transcriptions to become acquainted with the latest symphonies at home. But when listeners can now freely stream countless versions of Mahler’s symphonies performed by the world’s best orchestras, is this relic — one never intended for public performance — anything other than a curiosity or mere technical feat?

Schlosberg, in his program note, suggests that listeners could discover “unexpected details and structures” in this more intimately scaled version. But what came through more strongly in this performance was a sense of the Sixth Symphony as a mood piece. The duo offered a highly personal and subjective reading, full of shifts in color and tempo, with individual passages brimming with character: the manic frenzy of the first movement coda and the coiled energy of the scherzo.

Yet as Faliks and Schlosberg tackled this monumental, 80-minute challenge, they faced an obstacle beyond their control: the muddy acoustics of the West Garden Court, which obliterated inner detail. The pastoral interlude in the first movement, with Zemlinsky’s intrusive tremolos a poor stand-in for Mahler’s distant cowbells, could never hope to achieve a sense of cosmic stillness. Likewise, the dramatic structure of the finale disintegrated into large washes of sound.

Daniel Schlosberg. (Erin Clendenin)

The emotional weight of this most tragic of symphonies was felt only when the textures were thinned away: in the hauntingly spare lyricism of the slow movement and, most powerfully, at the conclusion, as the music burst with its final, horrifying crash and faded away into oblivion. The effect was devastating and most definitely Mahler.