at last, the UK is considering copyright reform that would make ripping a physical CD you own to your PC legal. It is currently illegal to rip a CD, thereby making your Sonos library illegal.
It is only an initial draft and will take years to come into effect, but it's a start. How far the act will go in allowing format shifting is undecided. 'One copy' is the proposal, but this would still make your iPod music illegal (if ripped from a CD), and you could not back up your digital library.
UK Copyright Reform