I'm trying to run the Arma2 demo and get the X3DAudio1_6.dll was not found messege.
After searching i found out i need to get the "directx_mar2009_redist.exe".
run the download which simply asks you where to extract it, tell it somewhere such as C:\Directx then when it's finished go into that folder and run the installer.
thats what i had to do