Short version: broadband itself does not need filters and works best without them. The filter is there for the phone, since you don't want broadband noises on the line when you're trying to speak on the phone. So I can see how running the broadband directly in to the test socket is better, and any socket you use for the broadband should be unfiltered.
Dunno what an "iPlate" is, but if it's a dual wall socket like this, then there's a filter on the phone side only:
