Connecting my Airport Extreme to my TV/ISP Modem

Dear all,

I will try to be as clear as possible. For me it is getting quite complicated but for somebody in the business there must be a clear solution to this matter.

The local ISP (Belgacom, the Belgian phone carrier) offers (like all ISP's these days) desides a landline an Internet and a TV HD connection. For that you receive, what they call a BBOX, a kind of modem which is also a router both ethernet and wireless.

The problem is that this router, especially the wireless, is very slow. So I decided to buy an Airport Extreme (Base Station) and an Airport Express (for in the other room to connect my hifi and my NAS).

On the BBOX (ISP modem and router) there are two "TV out" sockets, two ethernet and a wireless. The idea is to disable the wireless, and use one of the ethernet ports to connect to the WAN of the Airport Extreme. In that way I can create a wireless network from the Extreme (as base station) that has nothing to do with the medom/router from the ISP. I will only take Internet (as the Extreme is not a modem). I still need the BBOX functioning as I need TV. As the Extreme is an AC router I expect the wireless to be much faster.

But now I am confronted with the configuration of the Extreme. There are a few ways to do this: Bridge, DHCP and NAT, or DHCP only. Momentarily I am in bridge (this was the easiest way). So I suppose that I am still using the BBOX modem but just extending? When I chose DHCP and NAT it tells me that there is a confict in IP address and that I should set an IP address.

Does anyone have some ideas what the best way is to configure this? Grateful in advance!