Bundles of copper pairs link the two cabinets.
The old cabinet is retained as this is still needed for the voice and existing ADSL2+ services. It could be combined into one larger cabinet, but that would be mean larger cabinets and presence of mains when working on the lower voltage wiring might complicate things. Also it means no disruption to existing telephone services when the NGA cabinet is being rolled out.
Nothing special about the copper connection cable, its just a large pair bundle, with more added if needed.