As far as I know, you can’t have more than one DE in Antergos.
You need to re-install and choose during the install process.
When you think about it, it’s no big deal when you have a fresh install: just try a few over a few weeks and see which one you prefer.
Before doing this, check the documentation: the faq and google “antergos changing DE”
From the Antergos FAQ:
“Q: “What desktop do you give more attention to?”
We try to ensure all desktops receive an equal amount of attention. Though, its unavoidable that we’d find more things to “fine-tune” in the desktops we use on our own systems. Our project leader uses GNOME faithfully. I myself can’t stand it so usually I run Cinnamon. Though I have high hopes for the new KDE 5. If I remember correctly, the other two devs use Openbox and Xfce respectively. So really we’ve got most of the bases covered (well GTK-based anyway).”
Though this quote doesn’t explicitly rule out having 2 or more DE’s under the hood, it implies as much.
I loved my run with Antergos but am currently playing and learning in the Arch sandpit