The toy

If you want (very) good sound quality then you need a good DAC, and these are not cheap, although they're not as expensive as they used to be. But if you listen to low/medium bitrate compressed music, then yes, any cheap "plug" computer with an integrated soundcard would do. IMO an old netbook/nettop with a decent USB DAC/soundcard is the way to go if you don't want to buy specialized hw.

On a side note I've always preferred Logitech Squeeze * products over Sonos, but I guess I should have gone the Sonos way: Logitech EOL'ed their product range a few weeks ago :(