The wake word on Sonos for Alexa is still Alexa.

As a workaround, depending on which Sonos devices you have, could you configure Sonos Voice Control just on one of them and use Alexa on the other?

https://support.sonos.com/fi-fi/article/list-of-voice-requests-for-sonos-voice-control

It’s a shame you can’t embed one into the other: “Sonos, ask Alexa...”

This is an excellent question and has, I think, been answered.

Short answer: Use Sonos Voice Assistant and say “Hey Sonos Play . . . .”

My story of how i found that answer: 

in one room I have:

• An Alexa sensitive TV
• An Alexa sensitive cable box!
• A Computer (with the Alexa App!)
  and
• A Sonos1.  
• In an adjacent room I have an echo show

Dependant upon how loud I speak, any one of them seems to answer with differing results!

So what I have done is:

• Turned OFF voice control on the computer (Easy)
• When using the TV / cable box, I whisper into the remote control (which is where the microphone is! ~ daft but it works!)
• For the SONOS 1, I changed to “Sonos Voice Control”
  (which I found on the phone App!)

So far, I can now control just the Sonos system with the (automatic) wake word of “Hey SONOS” and it seems to work quite well.  The curse is the mad desire to have everything “joined up”.

The things that you can do with “Hey Sonos” can be seen here:

https://support.sonos.com/en-gb/article/list-of-voice-requests-for-sonos-voice-control

Oh, and by the way, You must use the “App” on your phone ~ the computer based “App” seems not to have the capability to change to the use of the Sonos Voice Assistant!

it had taken me far far too long to solve the puzzle ~ I hope this helps