I write in English, i hope you understand me. (else use Google Translation)
PX site is down at the moment, but i found a manual with google:
Look at page 12. It say's that the coupler has no IP adress from factory. It uses Boot P for getting a IP Adress.
You can find a program called IPAssign. I think it's the easy-st way. http://pxcfiles.com/Software/IPAssign.zip (or at PX web)
After that you can enter a website on the coupler, and see information from it.
Modbus TCP normaly uses Port 502 for communication.