BTW now that your brought it up, I did some further research as requested in the last thread and the term Nassi hador is brought in a non lubavitch Sefer kabbola called kehilas Yaakov.
There it states that Nassi stands for nitzutzo shel Yaakov avinu.
Just like Yaakov avinu had a neshama klalis that included the neshamos of klal Yisrael, in every generation there is a nitzutz of Yaakov which means this individual possesses all neshamos of his generation within his own neshama, and everything passes through him.