If you are worried about sound quality, forget about Bluetooth and use a direct connection using the RCA outputs to the line in adapter for the ERAs.

A single Sonos speakers will play both channels, but true stereo separation requires two speakers.

There’s a line-in adaptor available from Sonos, if the CD player supports that output? Or set up a music library and play from that. 

Thanks all, the line out adaptor was my first choice until I suspected that I would lose the stereo separation.

So it looks like I will lose something with just one Era100. Either quality, or stereo, or the cash value of a second speaker.

Going back to setting up a Music Library ? I presume I rip my CDs, then somehow Bluetooth them...does this maintain stereo capability on one speaker via the Bluetooth connection ? Does subscribing to something like Spotify give me stereo separation on just one speaker ?

Cheers.

You would not lose “stereo” sound with either the Bluetooth or the Line-In.  I put stereo in quotes because there’s not much stereo effect coming from a single speaker that is under 5” in width.

The music library could be on disc on your computer, or an NAS and access would be via your wifi. No Bluetooth or cables needed. 
 

Every time you say Bluetooth I ask myself why you want to use the poorest possible method of connecting? Sure it is there and built in but other options are (My ears are half dead so “reportedly”) superior and not unreasonably expensive.

I ripped my CD collection but kept an excellent CD changer as well as a single CD player. They were never used once I got the Music Library up and working. The players went out the door, the CDs are under a bed and my library meets all my needs.

​@Andrew McCletchie 

As was voiced by ​@Stanley_4 I don’t know why you want to use BT to play to the Era 100 as your main transmission when Line-in is the best. See the excerpt below from Sonos marketing regarding line-in and read more about it in this link

Moving on regarding stereo.  As ​@jgatie stated the stereo effect is limited by speaker size. Additionally, the stereo effect will diminish after about 6-7 feet for a single Era 100.

To put it into perspective if you were to use Era 100’s x 2 as a stereo pair you’d get good separation within a room approximately 20 x 20 ft (maybe even slightly larger). Placing the same speakers in a room 20 x 50 ft you most likely will only experience a “mono” sound at the far end of a 50 ft room.