been doing a series of tests regarding how to properly compute tangents between unity and substance painter.
thought i had everything figured out until i realized some information i was referencing was slightly out of date.
it turns out unity has patched in some new features, rendering a portion of my workflow which was essentially in place just to work around the absence of said features, no longer necessary.
i am still waiting to conclude nmy testing, but it appears that i can disregard tangents and binormals when exporting fbx files from maya. which in turn means i can let substance painter and unity calculate tangents using mikktspace basis. this also alows me to continue to use xnormal, should it ever behoove me to do so.