The Bluetooth device would need to be sending two signals, one right, one left. There is no way for Sonos to ‘pair’ speakers using Bluetooth. 

Since it is possible to set up two Era 300’s as a stereo pair and I have not seen anything about stereo speakers losing the ability to pass on bluetooth, I’d have expected the receiving speaker to regard the bluetooth connection as if it where an analogue connection and so play a stereo signal on both itself and the speaker it’s paired with. Are you saying it does not work like that?

I’m not sure I fully understand the original question here. If the Era 300 speakers are stereo paired then, when in range of their WiFi signal, they will continue to operate/play as a stereo pair, that includes whilst they are playing back stereo Bluetooth audio. The sending device (iPhone etc.) just needs to be BT-paired with either one of the Era stereo pair. The receiving speaker will do the rest and send the correct channel audio to the other speaker in the pair for playback in sync.

Hi

@Ken_Griffiths is correct. All you need do is enable BT on one Era 300 speaker in the stereo pair, connect your device and send the music. Both Era 300’s will play the same as when on WiFi (including sub if bonded to the pair) In short...”been there..done that” 

I think the confusion arose because the OP started out discussing the Move and morphed the conversation over to the Era 300’s which don’t behave the same as the Move/Move 2 in BT mode.

Note: In case your’re interested/wondering a stereo pair of Move 2’s on Wifi will join the party when grouped to the Era 300’s that are in BT mode. 

Indeed, for any stereo pair connected via wifi, whether it be Era 100, 300, Roam, or Move, bluetooth pairing will result in stereo playback on the pair.  It’s only when the Roam and Move are off the wifi network, and thus not stereo paired, that you can can’t play bluetooth to both speakers.

I’m not sure if the Era speakers can play bluetooth at all when not connected to WiFi.

A single Era 300, off WiFi, can play BT audio FYI …and just to clarify here, a stereo pair of Era 100’s, Era 300’s, Roam’s, or Move 2’s can play stereo BT audio to both speakers, when they are simultaneously connected to WiFi.

The earlier Move (gen-1) however cannot operate in both BT mode and WiFi mode at the same time - so that cannot be stereo paired in BT mode… and unlike almost all the other speakers mentioned here (except Roam), the Move gen-1 is a mono speaker only when operated standalone (unpaired).

Many thanks guys… it does indeed work… I was looking at visual signs that both speakers were fired up via bluetooth .. is blue lights on BOTH….

only when I played a music stream did I realise that they were both playing …. albeit with just one speaker with the bluetooth light on….

Yup so my bad...