From the Beo6 user guide :-
When you use Beo6 for 2-way communication with BeoSound 5, you must look up the IP address on BeoSound 5 first. Then enter the (new) BS5 IP address.
Find the IP address on BeoSound 5 by entering the NETWORK INFO menu on the BS5 and look up IP ADDRESS. The address could, for example, be 192.168.100.111.
Go to the Beo6
> Select Wireless in the Setup menu.
> Press Server IP on Beo6.
> Enter the IP address in the display and press GO
Depending on your setup, the IP Address of the BS5 can be changed periodically by the router. You can go into most routers and make an IP Adress fixed so it alway remains the same. Probaly they best solution for thiis setup.