The main "enemy" of boxwoods in the winter, if in their proper zone, seems to be wind. After that comes the winter sunscald, from warm sun hitting frozen leaves and thawing them. I would suggest that you make a screen of burlap, or other nearly opaque and somewhat wind proof material, and put it around the boxwood in late November or at least by mid-December. However, using piled-up pine boughs can also work.

In using the pine boughs as screening, be sure that they are placed such that they don't weigh down and bend the branches of the boxwood. Since you have done this before, I am sure you are well aware of this... I would imagine that the needles will stay on the pine boughs for most of the winter if they aren't disturbed - the dead needles would be loose, and likely to fall off the boughs if shaken.... I don't really think knowing the cultivar of pine will make any difference - I don't know of any pine species that are noted for dropping needles quickly when branches are cut, unless there is already a problem of needles dropping before the boughs were cut.