Question Author
There are two feeds to the sitting room from the quad-LNB to the PVR, and I can't see myself ever needing more than the 4 I've got.
There is only lighting in the attic and I am pretty sure I don't need an amplifier anyway. The aerial's above the apex of the roof and a good chunk of the relatively short distance to the transmitter (~12 miles) is open water anyway, with the rest of the way being obstructed only by a few trees and about a dozen houses. Only three televisions and none of them will ever need terrestrial HD reception, and analogue still hasn't been turned off, so the digital transmissions are low power. Watching more than one television doesn't have any impact that I've noticed on their signal quality (sitting room television always at 9.x/10 for everything) and it's only the two upstairs televisions which seem to struggle for quality and even then they're usually all right, though worse at night, I think. Normally both of them get the BBC channels at about 9/10, and ITV, Channel 4 etc. at about 6.5 - 7, just that the lower quality channels seem to have some sort of intermittent fault, from some radio interference or other, I'd guess.
Anyway, I figure changing the PAL connectors to F connectors, and swapping the two old cheap plastic splitters for one properly shielded splitter (satellite splitters are all well shielded, right?) at an early point in the wiring should cut out enough interference to make the signal good enough for what I need it for, so all I really want to know is whether the DC pass thing a feature that simply won't get used if the cables aren't connected to a satellite box, or if it will actually get in the way of using it is a simple splitter as I want.