FYI:
I made a factory reset on a new T100TA, used Microsofts function for making a bootable WIN10 USB stick and installed from that.

After install sound and brightness adjust via F5 and F6 was missing.

I downloaded the SOC driver package for WIN8.1 from the ASUS site and installed it and the sound is back to it's normal lousy volume(I then installed DFX sound app for normal volume)

Then I did the same with the ATK package and F5 & F6 are working.