Not sure exactly what you did.

You should have opened your Controller and seen the 300s in it.

Added the Arc Ultra to that system.

Unpaired the 300s if they were paired.

Added the left and right 300s to your Arc Ultra’s Room.

If nit what steps did you take?

Thanks for your reply Stanley, when I started the configuration of the Ultra I chose Living Room because that’s where left and right 300 are… but the Ultra is coming up Living Room 2  ?

Before you received the Arc Ultra, did you set the Era 300s up as a stereo pair in the Sonos app?

Do you want to now use the Era 300s as surround speakers with the Arc Ultra?

Yes I did set the 300’s up alone.. but thought the introduction of the Ultra would automatically configure into a surround layout 

If the Era 300s are currently set up as a stereo pair, you need to separate them as a stereo pair first:

https://support.sonos.com/en-us/article/separate-a-stereo-pair
 

Then under the Arc Ultra’s settings, select Set up Surrounds to add them as surrounds to the Arc Ultra:

https://support.sonos.com/en-us/article/add-surround-speakers-to-a-sonos-home-theater

I don’t know what you mean when you say you “thought the introduction of the Ultra would automatically configure into a surround layout” but it’s not quite that simple.

1. As long as the 300’s are set as individual rooms all you need do is go to the room with the Arc Ultra and select “setup surrounds”.
2. The app will see the 300’s and ask per speaker if you want to use the selected 300 as a surround.
3. Of course you select the “yes”option.
4. After the selections are made the app will play a tone through one of the 300’s while you face your TV and select the correct 300 (playing the tone) as either the left or right.
5. From than point the app/Arc Ultra finishes the surround setup.
6. The app even displays a graphic of the Arc Ultra and 300’s positioned as surrounds as a visual representation for ease of setup. 

Question: Did you not follow the procedure I just referenced 

Thank you Guitar & AJ been fast asleep it’s 5am here… as soon as I get the opportunity sometime today (we are moving in today) I’ll do as you’ve suggested.. can’t wait to get settled in and enjoy Thanks again for your help I’ll let you know how I get on 

All doneThank you guys, used the links on Guitars post and it worked a treat

Io ho fatto tutto con lo stesso sistema come hai detto, ma come si fa a ottimizzare poi il suono per la stanza? Non ci dovrebbe essere qualcosa? Grazie