‘It is the best thing I have ever done,’ said Mahler of his Eigth Symphony – for which the BBC National Orchestra of Wales and its Principal Conductor Thomas Sonderhgard tonight join forces with no fewer than five choirs. One of the grandest symphonic statements of the repertoire, concluding with a dramatic setting of the mystical closing scene from Goethe’s Faust, it’s mammoth scale matches the impressive space of the Royal Albert Hall. There will be no interval