Your second diagram is definitely wrong, you are passing through two filters to the router. This means that you are trying to get the ADSL signal from a connection that has been filtered down for the phone. If this is where you are getting the 64 kbs from, it is not surprising.

To get your second diagram to work you would have to move the filter to the other side of the 2way jack and plug the extension into one side and the filter into the other. You would then need another 2way splitter to connect the digibox and the phone. You will also need to plug the second digi box into the phone side of the filter, or connect it through another filter plugged into the 2 way.

To be honest, running a router through so many plugs and extensions is not very efficient and is likely to lead to all sorts of problems. It would save you a whole lot of problems if you use a powerline network and keep your router as close to the Master socket as you can. This way your whole electrical wiring system becomes your network, so you can plug in the adapters where ever is convenient.
Powerline Adapters