What do you choose as an opener for one of the grandest symphonies in the repertoire – a 75-minute musical monument that unfolds in vast arcs of thought and sound, demanding some 100 players? If you’re Andris Nelsons and the Leipzig Gewandhaus Orchestra the answer is simple, in every sense: one man playing solo Bach.

There are continuous threads running through this rather extraordinary programme pairing Bruckner’s Symphony No 8 with Bach’s organ music – faith, the transience of life, man’s frailty – but they are less striking than the tensions, the contradictions and conflicts of a concert that refuses any easy resolution.

The climax and culmination of Bruckner’s symphonic career, the Eighth is a monumental piece that conductor Wilhelm Furtwangler once described as a “battle of demons”. Although it moves from anxiety and darkness to radiant affirmation, the doubts are not so much resolved or forgotten as accepted, embraced into the whole.

This is music that is in Leipzig’s blood, but to hear it under the new music director Andris Nelsons (who took up his post last year and appears here for the first time at the Proms with his orchestra) is to hear it fresh. There’s an organic, forward-surging momentum to Nelsons’ reading; it’s an account that never loses sight of the wide-shot in the dense, gorgeous detail of Bruckner’s orchestration.

The Gewandhaus tone is a rich one (richer than ever, it seems, under Nelsons), but there’s no indulgence about it. Silences, gaps, the scrape and burn of those violent dissonances in the opening Allegro – these are what matter here in a performance stressing the discontinuous, the embattled, the irresolvable.

There’s a particular pathos to hearing Bruckner’s musical grapple after the certainty and immaculate symmetry of some of Bach’s greatest organ music. Anything further from St Thomas’s own organ that the Royal Albert Hall’s symphonic beast of an instrument is hard to imagine. With this is mind, Michael Schonheit (formerly music director at Bach’s own church of St Thomas’s in Leipzig) keeps things moving through the lovely chorale melodies of “Wachet Auf” and “Jesu, Joy of Man’s Desiring”, allowing the organ’s brute power some shock-and-awe release in the brooding Fantasia in G minor.

This isn’t Bach as the composer himself might have heard it, but rather Bach with a Brucknerian accent. But where Nelsons and the orchestra bring Bruckner into our own age – clean, energised, questioning – Schonheit allows more 19th-century affectations to creep in. There’s an expressive freedom to his bending and stretching of rhythm, to his ever-shifting pulse, but the results are far less satisfying, less emotive, than the urgent unity and precision of the Gewandhaus.