Coaxial cable has a limited life outdoors because sunlight and microbes cause the outer plastic sheath to become slightly porous and moisture can then permeate through, resulting in corrosion of the metal...
If you upgrade from an ordinary Sky Digibox to one with more than one dish input (or you want to add another digibox) you will need a quad-output LNB or an OCTO (8 output) LNB for your dish. A Sky minidish LNB...