Speedtouch 716 setup

I'm having a few problems getting my 716 to work properly with my xbox360.
If I just use the standard NAT setup then I can connect to live, connect to my media centre box upstairs, and play most online games... except a few Electrions Arts ones (Burnout Revenge, Fight Night round 3)

As a workaround I can assign the 360 my public IP address - I can then play on the EA servers however because its not getting a lan address anymore it can't see my media centre pc.

I have tried adding the "xbox live" application/setting thing to the 360 in the router webpage but it makes no difference.

Is it possible to keep the 360 on the lan but have all traffic sent to it by default (unless of course marked by NAT, upnp, or whatever to go elsewhere)? If anyone can help I'd appreciate it

*bump*