The Sky upgrade converted the existing multi-switch communal system to what is referred to as Single Cable System.
The SCS device requires to be connected to Sky receiver with SCS capability.
This is a software development where the Sky receiver sends commands to the SCS to request your specific channels.
The SCS delivers all signals in a narrow band that the Sky receiver is set to. Very different from delivering the entire band to the Sky receiver.
The splitter is a "smart" device and allows a second Sky receiver or a second port on a Sky+ receiver to be connected. Each port receives a different SCS channel.
If you are into the tech detail, try searching the web for Unicable or SCR , this is a European Standard for this technology and is now about 7 years old.