There are a number of ways to do this, you could use the Connect:Amp line-in with an Airplay2 Airport Express and target the ‘Connect’ in that way and group the playing Airplay2 audio with your other Sonos devices.

Or if the Amp’s line-in is already committed to using another audio source, then you could add an Airplay2 compatible Sonos Speaker instead and target that with your Airplay2 audio and then group that with your other Sonos products. However…

Note: if you are currently using your devices in an S1 Sonos Household, that a new Sonos One SL is not compatible with S1 Systems, but you can still use a Sonos One (gen2) speaker.