What HiFi is connected to the Connect Amp line in?

Do you have any other SONOS products?

If this is to add voice control rather than Bluetooth, the Dot does not need to be cabled to the Connect:Amp at all.  What are you trying to do?

I am puzzled by your having a hi-fi connected to the line-in on the Connect:Amp - that’s rather unusual.  Could you explain a bit more?

I have the hifi connected to play cassettes and cd etc, and use the Sonos amp and the browse line in so I only have the one set of speakers.  I do have a play bar for them in the lounge and a play 3in the bedroom.  I was thinking of using the echo dot to control everything by voice, rather than clicking everything, suppose I was just been lazy lol I would add all the Sonos products are series one

You don’t need a wired connection from the Dot.  The article linked below will explain how to set up

You can also use Alexa groups to make an Echo Dot play on a particular Sonos device by default.

https://support.sonos.com/en-us/article/set-up-an-amazon-alexa-device-to-control-sonos