It isn’t often that the Musikverein programmes Webern, the most underperformed of Vienna’s major musical sons, alongside a Liebestod from Bayreuth’s reigning Isolde, but then this was no ordinary Musikverein concert. The Gustav Mahler Jugendorchester is currently on their annual Easter tour and the programme on Thursday night, while eclectic in appearance, was consistent with their commitment to the European late-romantic and modernist traditions.

The conceptual underpinnings were plausible enough on paper: Zimmerman unpacks and expands Webern while preserving his tightness of motivic construction; Scriabin gives Wagnerian themes of longing, will and self-assertion his distinctive impressionistic, mystical gloss. In practice however, the strongest impact made concerned three big climactic high-points, and the way they bring about endings which attempt to rise above earthbound musical finality. Wagner does this by packing Isolde off to the eternal bliss of self-obliteration (as Slavoj Žižek once put it); Zimmerman with a ‘never-ending’ intensification of sound’ (his description); and Scriabin by positioning his radiant ecstasy of C major at the end of the Poème de l’Extase as a transcendental breakthrough. One constant at the Gustav Mahler Jugendorchester, which auditions every year, is their massive forces – forces which dispatched these epic culminations with astonishing power and vitality.

One shouldn’t complain about hearing Webern in the concert hall, but the Wagnerian connection was at its most tenuous here and his Sechs Stücke, Op. 6 were in truth a bit of a warm-up act in this scheme, which strikes me as the wrong way to go about performing these intricate miniatures. Numbers were off as well: by my count more horns than Webern requested but two trombones too few, and strings well in excess of the forces specified. It was not pedantic of Webern to stipulate the numbers he did; even small changes to woodwind and brass make a noticeable difference in balance. The Gustav Mahler Jugendorchester is about giving the maximum number of talented young musicians the opportunity to play that the bending of symphonic convention will allow, but in this instance the decision to interpret Webern’s ‘large orchestra’ loosely led to a thick sound in the strings and a corresponding loss of transparency across the ensemble.

Those strings – all 86 of them – were however on stunningly luscious form for the Wagner, with a good deal of perceptively shaped ebb and flow before the eventual unstoppable surging. Conductor David Afkham’s tempi were on the brisk side, but proportions were fine and his command of detail impressive. Singing the Liebestod in concert with these kind of numbers is no enviable task, but Iréne Theorin made herself heard throughout without so much as a hint of forcing, cutting through the orchestral texture or floating above it in ways that worked both for her voice and the music. There was lots of vibrato above the break and some graininess lower down, though these were not the ideal circumstances for tonal colouring; in compensation, there was her smooth transition from a somewhat rhetorical style of delivery at the beginning to a state of serenity for the final phrases.

Both the Zimmerman prelude for large orchestra Photoptosis and Scriabin’s Poème de l’Extase were rich phantasmagoric collages in their own highly individual ways, with good ensemble and some vivid solos, particularly the solo trumpet who played the repeated motive in the Scriabin (labeled ‘self-assertion’) with appropriate insistence. The one thing I missed in the Zimmerman was quarter-tones where we should have heard them, but it is a minor complaint. As the orchestra’s assistant conductor (replacing an ill Ingo Metzmacher for this tour), David Afkham rehearsed this programme in the pre-tour residential course, and his tutelage has clearly been thorough. On the podium he is a disciplined conductor with a sharp ear for the music’s expressive potential in moments big and small, and it will be interesting to see how his career develops.