The Diotima Quartet claim the first recording of the new Bärenreiter edition (not yet published, to my knowledge) of Janácek’s Intimate Letters Quartet. And this is no small matter of the odd slur, dot and accidental. Whole phrases come out with startlingly unfamiliar textures and tempo relationships; the floaty five-note downward scale motif in the second movement is no longer in regular whole tones and only has four notes; sundry bowed notes are now plucked, and so on. Performers have always had tough choices to make in this piece; from now on they’ll be even tougher.

There’s apparently even an option for the end to be played stratospherically on the viola rather than merely high on the violin, which is what the Diotimas do in their reconstruction of how the piece might have sounded with Janácek’s programmatically inspired notion of using viola d’amore instead of viola. That conclusion defeats even an exponent as fine as Garth Knox (and curiously the end of the “straight viola” recording is also unhappy, with unwanted open-string resonance jarring against the D flat major tonic). But elsewhere Knox wields his instrument to wonderfully expressive effect, its sympathetic strings creating their own magic halo and drawing the ear even when the instrument isn’t carrying the main line.

The Kreutzer Sonata is just as carefully prepared and as full-bloodedly executed; however, issues of text and instruments apart, I wouldn’t trade in the superbly passionate Pavel Haas Quartet’s Janácek recordings, because by a small but definite margin the young Czechs are more liberated and give a feeling of being more inside the music. That said, the Diotimas’ double initiative, on top of their always classy execution, makes this new disc indispensable to the Janácek aficionado.