An excellent guide how to set up DC++ for the U2 Hubs can be found here.
If you are in passive mode because of a router and a changing IP adress this is how you should manage to get active:
Enter you hostname in the IP field of the settings.
Don't forget, that the Dynamic DNS service needs to know your new IP adress every time it changes. This can be done in either by a special software or by your router which is the easiest way (not all routers have this feature though).
Note: this worked for me... no guarantee that it will work for you :)