It's against the Sky T&C to use a router other than the one they supply. However, you can get the password from their router and program your own router if you know how, breaking the terms of service.
Quiet line test is very quiet and I have SNR margin of about 10db after new modem and filter. As I said, problems are solved, but I'm trying to figure out what will happen if I join Sky, ie what will their router be (any good?) and will I be able to continue with my current router without action being taken against me?