The RT5000 doesn't have an IP or MAC address, the interface card plugged into it does.
Problem is there are more that one compatible interface card. AP9617 and AP9619 are both compatible.
Also the IP can be changed so if it's been previously configured you have two kettles of fish to swim through.
Here is the setup guide. It covers both interface cards.
http://www.apcmedia.com/salestools/ASTE-6Z5QDZ_R0_EN.pdf