I would perhaps check and ensure that the Amp has a ‘unique’ name and is not the same name as an Alexa group and is not named the same/similar as anything else in the Amazon Alexa list of devices.

Set the default music service in the Alexa App and ensure that same music service is also installed in the Sonos App with the same login credentials.

Next remove/reinstall the Sonos Skill in the Alexa App and rescan/discover all the local Sonos devices.

When scan is complete, then see if the Amp will work with Alexa.

So if the Amp was called ‘Den’ (just as an example here) then try playback with an instruction that’s something like this  ‘Alexa, play some music on Den’ and see if it the connected speakers then play.

Thanks, will try all of that.  Certainly appreciate the feedback.

Figured it out.
 

 First, dumb me, we had a power outage and for a bit the amp supporting the “House” speakers was down.

 Second, when Alexa scanned for devices she found “House Sonos” instead of the Sonos “House”.

Easy solution. When we want Alexa to play through the house speakers we ask her to use House Sonos.

Knew it would be something simple.