So basically replacing a single LNB for a quad then allows upto four seperate boxes, unless you're using Sky Plus which requires two per receiver. Is that correct? And each receiver requires its own seperate cable, similar to Ethernet really. One cable per computer.
LNB (Low Noise Blocker)
The LNB is the component located at the end of the arm projecting from the satellite dish. It receives the signals sent by the satellite ("Ku-band") and converts them to a lower frequency (3.7-4.2GHz) that can be accepted by a compatible satellite receiver. LNBs send this converted signal to the satellite receiver via RG-6 coaxial cable. Satellite TV providers have multiple satellites in various orbital positions, and a separate LNB is needed to access each satellite position.