ok so this pretty much basically explains the thing about the textures.

bsm - albedo/base/diffus texture.

nrm - mgsv's/fox engine's normal map, which uses the green and alpha channel instead of the red and green channel.
these have been converted to the blue/purple color by copying the alpha channel to the red channel, inverting the green channel, and making both the alpha channel and blue channel completely white.

srm - mgsv's/fox engine's specular map. you'll notice that there is "_r" "_g" "_b" at the end of each texture name of the srm.
that's cause the srm was originally channel packed and got unpacked into separate textures.

the "_r" was the red channel of the srm, it is a specular occlusion/specular mask 
the "_g" was the green channel of the srm, it is roughness that is inverted. 
the "_b" was the blue channel of the srm, it is a cubemap mask.

mtm - material parameter map. yeah I don't really have much knowledge about it.