You can find the speakers that are compatible as surrounds for the Ultra here:

https://support.sonos.com/en-us/article/surround-sound-guidelines-and-limitations?product=arc-ultra

Only symfonisk gen2 is mentioned on the ultra compatibility page… does this mean that i should cancel my order for the arc ultra? I have the gen1 symfonisk. Didnt even know there was a gen2 version.

Have tried with the gen1. It wont discover the gen1 as surrounds. 

Bleh.. maybe we’ll go for the old arc then.

was super stoked for the ultra but cant be arsed to replace my surrounds for that 🥲