For those interested in classical and jazz music I would recommend a free trial to the Presto Music streaming app currently £10.99 a month. Their extensive database is professionally organised and can be air-played to Sonos devices via a superior iPhone or tablet interface. Many of their streams are available in hi res. for those with other high end equipment.
You should talk to Presto about adding Sonos to the streams they offer.
https://docs.sonos.com/docs/content-service-get-started
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