BRL - I was told that the filter had to be fitted between the wall socket and doubler.....
So, my upstairs extension has the straightforward filter (similar to yours) plugged into it with the 'normal phone' (RJ11) socket connected to the cordless DECT base station and the ASDL modem connected to the modem port. Actually it's a wireless modem so I can use the laptop anywhere in BEagle Towers...
The downstairs socket has another plugged in; nothing connected to the modem port but a doubler connected to the RJ11, one socket used for the Sky receiver and the other for the phone/fax machine.
The ASDL light stopped flashing and changed to steady yesterday; for a few minutes I had home wireless broadband internet access but I suspect that the 'system' recognised that my ISP change-over date isn't until Monday, as it closed down a bit later..... But the browsing speed compared to dear old 45.2 which I usually get was truly excellent!