From the AD-8X installation manual:

"Setting a static IP address is NOT necessary and is discouraged. The RTI two-way driver uses the UPNP name of the AD-8x to find it on the network so a static IP is unnecessary."

Is this not accurate?

I am 99% sure the AD8 itself was set to DHCP (it's static right now just from me trying to troubleshoot) but you may be right about a DHCP reservation in the router. Unfortunately it's smoked so I can't look it up.

In theory, if I had a copy of Integration Designer, would I just connect to the XP6 via USB and download the program file? Then somewhere inside the file it would show what IP it expects the AD8 to have?