There should be no additional amplification necessary between the RCA output of a CD player of any type. Are you using the output from the RCA jacks on the back of the CD player, or perchance the output of a headphone output from the CD player?

The challenge is that if the output of the CD player is ‘twangy’, that’s what the Sonos would play. Have you reconnected and tested your turntable? If that plays properly, then it’s not the Sonos. If the turntable also sounds ‘twangy’, it’s the Sonos. 

Hi Bruce, 

Thanks for your reply. 

Im using the RCA output. Turntable sounds perfect. 

I have been playing with some settings, I adjusted the Source Level from 10 to 2. This seems it may have resolved the audio quality issue for the CD play. 

Im not sure what this setting means, but I will now test that with the turn table and see how we go.

Thanks

Dave

That suggests the line level output is different on the pre-amp and the CD player, and you may have been over-driving the input at level 10. Although I’d have guessed more at distortion than twangyness. But I suppose it could manifest in slightly different ways, and ‘twangy’ is, as you suggested, and odd term. I’m glad you resolved the issue. Be aware that there is slight variations between ‘line level oytput’ on various devices, although it should be relatively small. You should be able to find a setting that matches both devices well enough. 
 

You may want to check that your pre-amp on your turntable matches the type of stylus. Moving Magnet vs Moving Coil, and all that.