A question about differential ended settings for single ended inputs
The resistor establishes a common mode voltage that is within the range of the amplifier. 

You could also use two 10K resistors, one from each input line to LLGND. That would load the signal differentially but would retain balance. Grounding one side or using one resistor does not load the differential signal but makes the input more like a single-ended input (in the case of grounding it, exactly like a single-ended input) so you lose some of the advantages of a differential input. 

The value of 10K is not magic. Values as low as 50\$\Omega\$ are used sometimes- just enough to prevent serious ground loops in the case where the grounds are not isolated from each other. That's called a pseudo-differential input.