I would assume that you could just plugin your LFE track straight into one of the inputs on the SUB, It looks like internally it sums the lower crossedover audio from the L and R and spits out the upper through the XLR outs. So just ignore all the other i/o and use it like any other single input sub.
There are a couple different surround track orders:
L, C, R, Ls, Rs, LFE
The ITU Standard, L, R, C, LFE, Ls, Rs
and I'm sure there are a couple others… just make sure your daw is set the same as your speaker outs