How do you turn a Requiem into a stage work? With some difficulty is the answer. Famous settings by the likes of Mozart, Verdi and Britten have an urgency and scope that makes them loosely viable as theatre – which is why you do occasionally find them done dramatically rather than in a concert hall or church. But Brahms’s Ein deutsches Requiem, which does away with the traditional liturgical texts and replaces them with consoling reflections from the psalms and other biblical sources, is a different matter. And however Brahms envisaged the performance of his piece, it won’t have been on the terms in which it was given recently at La Seine Musicale – the spectacular concert hall that floats like a ship in the middle of the river in Paris (it is actually an island) and where the French conductor Laurence Equilbey puts on extraordinary projects with her period-style ensemble Insula.