When they burst onto the chamber music scene in the 1970s, the Emerson String Quartet were iconoclasts. New York-based, they swapped first and second violin roles, and along with the Brodskys and Kronos they swept away the grand but stuffy tradition embodied by the Amadeus and the Guarneris.

And now, nine Grammys later, they’re continuing to push the boundaries with an intriguing CD featuring the bookends of arguably the most momentous decade ever in classical music.

Joined by long-time collaborators, American violist Paul Neubauer and British cellist Colin Carr, the Emerson’s readings of the great sextets by Tchaikovsky and Schoenberg are like a lesson in musical history. Tchaikovsky, at the beginning of the 1890s, used his Souvenir de Florence (the slow movement was written in the city) to continue the classical traditions that he inherited from his models Mozart and Mendelssohn. Then, at the end of that decade – indeed century – the young Schoenberg in his Transfigured Night sent music into the future, his twisted harmonies depicting haunted forests and psycho-babbling sensualists.

And in this wonderfully-played CD, which is being hailed as a farewell for cellist David Finckel who’s leaving after 34 years, the Emersons and friends do everything to heighten the different musical universes of the works.

In the Tchaikovsky, they play out, so engaging and almost in your face, as if they’re one of the young-gun quartets like the Ebènes, for instance, who have now inherited their mantle as the young tearaways (and perhaps even exceeded them in the wow- factor). There are plenty of venerable recordings of Tchaikovsky’s late- career sextet, but few can match this one for clarity of texture, and sheer joie-de-vivre, as if to indicate that Finckel is leaving on good terms and in the mood to celebrate a great career. Not a farewell, then, but a life-affirming performance.

But then the universe changes, all the bubbles float off into the ether, a cold night falls, and we’re in a moonlit forest outside Vienna. On this evidence, you’d imagine the opening to Schoenberg’s Transfigured Night being marked ‘misterioso-to-the-max’ but what’s on the page doesn’t matter because this group of master-musicians clearly aren’t playing the notes; they’re playing the meaning underlying this extraordinary expressionist work inspired by poet Richard Dehmel.

The Emerson Quartet will go on with Paul Watkins coming into the cellist’s chair, but in this triumphant recording they have sent Finckel out on a high.