A couple questions first. What kind of armor mod is this? Did you build it from scratch or is it an edited version? If you're just editing it a bit (moving meshes, cutting off pieces, etc.) then you should try and stick with Outfit Studio. If you're trying something more fancy, then what you can try is finding the Oldrim version of the file and importing that into blender. Outfit Studio will auto-optimize Oldrim files for you when you import them! It's a pain in the ass that the nif addon doesn't apply to SSE yet (like seriously?). Would you mind telling us what armor it is, or if you're making it from scratch? Also, try this link on how to export https://wiki.beyondskyrim.org/wiki/Arcane_University:Blender_2.7x_Export