Are you sure the mic is deactivated on the Beam?

I was under the impression the One would have its microphone disabled when added as a surround due to the Beam being voice enabled. 

The only way for the Beam not to duck is to use an Alexa device that is not part of the Beam setup.

Errr you seem to be right !

I thought I deactivated the mic on the beam but actually it didn’t !

If I understand well, a One SL would have been enough in my case…

I find it annoying that you can’t chose the device to use with Alexa !

Correct, two One SL would have been sufficient for you. If you ever add additional speakers you could buy a One SL, then move the One to another room.

Even if you could use Alexa on the One with the Beam, the Beam would still duck as the ducking applies to the Sonos room, not the individual speaker within that room.

I think a simple Echo Dot would be appropriate for your kitchen area.

I just have something that makes me wonder.

As you can see in the screenshot, Alexa is only installed on the sonos one, not on the beam.
When I ask “Alexa, which time is it ?”, it’s the sonos one that answers me (the mic is well activated, I whisper very quietly and far away from the beam).

So I think the only problem is the ducking on the sonos beam...

That looks like a bug with the current software.

Surrounds should have their microphone disabled when used with a voice enabled soundbar. This is listed under the Limitations for surrounds.

Maybe it’s because I had Google assistant first installed on my beam, then I added the One and Alexa on it.

That uninstalled Google assistant on the beam and didn’t replace it.

I’ll try to keep that way, it works fine with me, too bad for the ducking !