Why not just add a Sonos Five speaker(s) and just add your HiFi/CD player connected to the line-in port? That way you can play to any/every Sonos speaker in your Household and have a great speaker too for the money. Seems to be the best value to me, unless you already have a pair or ‘active’ or ‘passive’ speakers about the place, in which case you could maybe opt for the Sonos ‘Port’ or ‘Amp’ instead, respectively speaking.

Either would work fine. Plus passive speakers, of course.

I think you would get a better result from a Sonos Amp, given the same budget. 

I wouldn't buy a CD player, though. Sonos is designed for music files not physical media. I suggest you rip and / or stream. 

Ken's response prompts me to suggest you consider a pair of Fives as another way of getting excellent stereo sound.