London Sinfonietta, Royal Festival Hall / Queen Elizabeth Hall, London

The London Sinfonietta's sell-out Festival Hall show, under an unflappable Stefan Asbury, boldly interleaved the Sinfonietta's usual fare with arrangements for the band, mainly by David Horne and Morgan Hayes, of music by the Warp label artists Boards of Canada, Mira Calix, Aphex Twin and Squarepusher. But if the audience for the opening of the second Ether festival was going to be open enough to take seriously "the coming together of two different musical worlds which have much in common", then why did the girl in front of me spend the evening tittering and texting, apparently oblivious to any of the delights of this 21st-century smorgasbord?

Neither Ligeti's masterly Chamber Concerto (with video accompaniment that was, for once, at least sometimes relevant and not merely distracting), nor Rolf Hind's selections from Cage's Interludes and Sonatas for Prepared Piano (its colours, like the counterpoint of the Ligeti, distorted by extreme amplification) made the impact they should have. What Simon Haram's "easy-listening"-style saxophone realisation of Karlheinz Stockhausen's Spiral had to do with the radical nature of this work's conception, heaven only knows.

And though well-crafted, the new orchestral arrangements of Aphex Twin and the others had me wondering just what was the point of making instrumental versions of electronic music; you wouldn't dream of doing this to Stockhausen's early tape pieces, would you? Only Sound Intermedia's version of Mira Calix's Nunu, an intriguing and disturbing piece based on the sounds – and, on screen, the far-too-magnified-for-comfort sights – of insects brought all its elements convincingly together.

The Sinfonietta returned to business as usual with its programme at the Queen Elizabeth Hall, under Thomas Adès. This ensemble's business is, however, changing even in its more regular programmes, and what we got here was a series of personal post-modernist takes by three British composers and one Italian, unrelieved by anything really hard edged.

When this works well, as it did with two typically idiosyncratic scores from Gerald Barry (including his 1992 Sextet), and with Niccolò Castiglioni's Quodlibet (a scintillatingly scored little piano concerto in which Nicolas Hodges was the alert soloist), this can be very persuasive. When inspiration seems more fitful, as it did with Judith Weir's new Tiger under the Table (in which solo bassoon and trumpet play like characters out of one of this composer's operas), it can at least be rather diverting. When it doesn't work at all, as with John Woolrich's suite from his theatre piece Bitter Fruit, it's just empty showmanship.