Apple Airport Express - speaker group?

[audi321]

Hi all, long shot I know, but I have a couple of old (Gen 2) Airport Express (A1264) plugs, and although I can airplay to them, I seem to be only able to play to one at a time. Is there a a way that anyone knows of to create a group to play them at the same time?

They're on the latest firmware, so Airplay 2 enabled.

Thanks all for any help.