Does that one speaker have a microphone? If not, while you can control that speaker from any of your other speakers, it cannot, itself, have voice control installed on it. 

You describe the speakers as being ‘different’ - what model speaker is it that you cannot add the voice assistant to? Note that not all Sonos products have a voice assistant feature - one of the easiest ways to discover if it supports an assistant, is to look for the mic symbol on the top of the device.

If you post the name of the speaker model I, or someone here, maybe able to say if it supports installing a voice assistant - note that if it doesn’t, it can usually still be voice-controlled by a product that has a voice assistant installed.

I have a Sonos ARC, Sonos One, Sonos Beam and a Sonos Move.  The Sonos One is the speaker that did not come up on the menu as a candidate to be added to the voice control.  The other three speakers appeared on the set up menu and allowed me to add them to voice command system.

I did notice that the Move has a microphone sign/picture on the top of the unit.  But, the Sonos One speaker does not.  Based upon your comments, maybe the Sonos One is not capable of being controlled via voice commands.

I have not tried using the voice command yet.  Again, based upon comments from both of you, might I be able to control the Sonos One through some of the other units via voice command?

More than likely it is a One SL, which does not have a mic, so it is not voice capable.

Look at the base of your “One” to see the product name. You will likely see “One SL” which as previously stated doesn’t have a mic.

Yes, by using the name of the Sonos One SL’s room, you can control it via the other devices via Alexa.

I actually don’t have any mics on my Sonos turned on, I use Amazon Dots to control them, when I feel the need. At some point, since I don’t really trust Amazon that much, I probably should turn on SVC, since I trust Sonos more not to be eavesdropping and selling my data…

Thank you for your help.  Much appreciated.