[Chris]

You have a quad-LNB already ... well fine, that's half the battle. Are you saying you have also wired a third piece of coax into it, so that you have the original dual Sky+ installer's cable, plus your own DIY cable, attached to the LNB at the dish?

To be honest, if you have a pair of redundant Sky+ cables sitting in your living room, and a new Freesat box in need of a feed from the dish, I'd just use one of the Sky+ cables for the time being. They are quite interchangeable between Freesat and Sky boxes. I've successfully run a Freesat box on my own Sky installation.

Unless you're competent and confident, you risk a poor-quality connection between your coax and the LNB at one end, and coax and the f-plug connector on the other end. Also, I don't like the sound of 'brown coax' - that sounds like regular terrestrial aerial cable, and is lower quality than the sort you should be using for a satellite installation.