The two are not related. Unicable / Unicable II is a switching protocol, just like DiseqC, and using a similar signaling mechanism.
OpenPLi can do that on any tuner, but not every version has the same features, I can imagine that there isn't much support for switches or setups with lots of SCR's in OpenPLi 4.
The FBC tuner (Full Band Capture) is originally designed for a Wideband LNB, which has two outputs, H and V, but no separation in frequency bands. Hence you have two externally connected tuners (to those two outputs), and 6 that can piggy-back on one of those two, for recording. For this reason you'll see for example the SKY Q box advertised as a 7 tuner box (watching + 6 recording), as they reserve both A and B for watching.
Since signalling is software, Enigma also allows you to connect other things to an FBC tuner, or even split the two inputs over two different systems (I have one connected to my own switch, and one connected to the buildings GSO).
Currently in use: VU+ Duo 4K (2xFBC S2), VU+ Solo 4K (1xFBC S2), uClan Usytm 4K Pro (S2+T2), Octagon SF8008 (S2+T2), Zgemma H9.2H (S2+T2)
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