As for splitters, they shouldn't affect communication between the gateway and media extenders. As the above poster stated, it's all about signal. A "dedicated line" doesn't make any sense. You're free to move the gateway around as you like as long as the signal in your home is fine. What's generally NOT recommended is installing an Amp on the line before the gateway, but that isn't your case here. To check your signal levels (the easiest way), you'll need to be connected to the gateway with a computer/smart phone (anything with a browser). Visit »192.168.100.1
and your upstream and downstream signal levels will be displayed. Although I'm currently at work and cannot test the following, the Media Gateway should have an OSD menu that can be accessed by holding the menu and OK button on the box itself, then using the remote to navigate. Signal levels for the device should be displayed somewhere in there.