I have always wondered the difference and now found the answer so i thought i'd share it, as i'm sure it will help others too.
A QUAD LNB gives you 4 independent LNB feeds which can receive switching signals from 4 digital tuners and allows the full range of tuning options to be used. These being Horizontal, Vertical, High Band and Low Band.
A Quatro LNB has 4 outputs each one represents one of the 4 tuning options as mentioned above.
The 4 outputs of a Quatro then feed an IF distribution system which in turn then feeds X amount of digital tuners, this system is used for communal systems.
There is no two output version of a Quatro for the reasons given
The Quad LNB is in fact 4 seperate units in a single housing each with an independent connection to the digibox tuner. The tuner then sends commands to the LNB which sets the H/V and Low/High band status and since each of the four LNB units in the housing are independent they can be tuned to a different transponder at the same time.