because they rearranged how multiple audio channels work on w10 and claimed it is superior to 8.1's way, so you now got stereo
there's no info regarding this other than that, if you can take a hint, 5.1 audio recording is not high on the list for "businesses"
edit: just asked the proshot guys if they could implement 5.1 audio, they said OS controls the microphones and doesnt let developers do much with it
so no hope for 3rd party solution