Trying to get my head around this before I give advice elsewhere. Is based on single satellite systems. Please feel free to comment / correct my errors
How The signal is split
Satelite singnal comes 2 pairs Horizontal (H)/ Vertical (V) and Positive (P) / Negative (N). So there are effectively 4 signal areas HP, HN, VP and VN.
Each channel is on a transponder, each transponder is on area as above.
Universal LNB
The old LNB that we all know, can have 1 to 8 outputs with each output having access to 1 transponder.
Unicable LNB
Only has one output (although may also have additional Universal outputs) These combine the 4 areas (as above) into one sending it all in one cable (think of this in the same way as a terrestrial aerial) you can then use splitters to spider around the house, e.g. you could have a 3 way splitter for 2 inputs to your receiver and 1 to your TV. Its a much neater solution.
Standard Tuners
Each Tuner needs its own feed to the LNB, and is capable of watching / recording all channels on the same Transponder (need verification for this)
FBC Tuners with Universal LNB
These have 2 physical inputs for there 8 tuners, you can either have 1 or 2 feeds coming from the LNB with the other 6 or 7 virtual tuners being fed from the same input. These tuners have quite an advantage even with a Universal LNB in that the virtual tuners are not limited to just the same transponder as the lead tuner but instead can access a whole area as described above. This means with 2 feeds you can watch / record around 50% of the channels available to you.
FBC Tuners with Unicable LNB
You only need a single feed but can use 2 if you prefer, the virtual tuners will pick up the signal from the physical but then act independently, this gives all tuners access to all available channels on the satellite.