Hi @Neiltoo.

Welcome to the Sonos community and thanks for reaching out to us. Allow me to share some information to help out.

Allow me to share with you the guide about Control Sonos with Amazon Alexa so we can better understand what is and what is not supported with Alexa on Sonos. 

If I add 2 x Sonos One SL to my Beam as rear speakers will Alexa play music through all 3 speakers or just the Beam? The audio with be generated by the entire Sonos home theater system (Beam and 2 Sonos One Sl). Once 2 Sonos products are added as surrounds/bonded as surrounds to a Sonos home theater speaker, it cannot be used as independent audio to the Sonos home theater speaker it is bonded to which in your situation is the Sonos Beam. The Sonos Beam is communicating and receiving data on behalf of the surrounds (and sub if applicable).

I hope this helps.

Please let me know if you have any other questions or concerns. I’ll be here to help.

Thanks,

Many thanks for the very quick reply. That is very helpful and what I hoped to hear. 

Thanks again