I have a Labgear 8 way(? - I think it's 8 way, can't be bothered to go and
look) amplifier in the loft. I have a coax feed from the back of my Sky
box
up to the loft, and I use a simple 'Y' connector to combine the feed from
the Sky box with the feed from the normal aerial. Works quite well.

Doesn't that cause ghosting?
Or isn't there an aerial connection from the splitter, TO the shy box?

Sparks...