It’s an old Airport Express, not an Apple TV. Could it be that it’s not supported?
Ooohhhh. The old one. I don’t think that model works very well with Roon.
I don’t know the exact details of what makes it different (we have never seen one–Roon is about a year old, and that product turns 10 next year).
Apple did a pretty serious re-working of the AirPlay protocol in ~2011, and every Apple device sold since (and every non-Apple AirPlay device sold, period) speaks the new way. We speak the newer protocol version too. iTunes likely has a specific set of code for talking to this one device.
Maybe there’s a way to update the firmware in that device so it behaves like a newer one? If not, I’m out of ideas 
As with anything else, If we got enough feedback on this, we’d do the legwork to make it work.