Usually, whenever we need to do some real-time messing with the Sample Start, we usually discard the NN-XT (because there's no way to automate it's sample-based Start/End, and Loop Start/End settings) ...
...and think immediately of the NN-19 because it has, right there, on the upper right corner, a little knob to easily tweak the Sample Start, controllable through Combinator's modulation routing matrix...
...but, there's a way to do the same thing with the NN-XT, indirectly :P
There's a NN-XT setting that can be used to do exactly the same thing and be as controllable but through CV and affect all the loaded samples at the same time. :)
Turning the NN-XT's Velocity S.Start all the way to the right will mimic the NN-19 Sample Start behavior, controllable by the CV values sent to the Gate CV input at the back of the NN-XT.
Now, imagine using Thor's Sequencer Note and Gate/Velocity CV outputs to control the NN-XT (or a NN-19 inside a combinator) taking advantage of the high rate resolution... can you see what's possible to do ? ;)
BTW, NN-19 reminds me of
Paul Hardcastle's "Na-Na Na-Na Nineteen"