As known, nVidia's VGA Cards cannot enables HDR with Antialiasing becouse the Hardware is used for both operations and AntiAliasing overwrite HDR or HDR overwrite AntiAliasing...
but in Half Life 2 Lost Coast, nVidia Cards can enable both of them becouse Half Life 2 uses different way to calculate the HDR simultaneusly with AntiAliasing.
HDR without AntiAliasing is useless
please, try to implement the HDR with AA also for nVidia Cards like Half Life 2...
so, why disable Antialiasing if i choose HDR Rendering?
I think it's true, in this way I can understand why if I force Antialiasing from outside game (see RivaTuner software or nVidia Driver Panels) in-game Antialiasing is not applied also if I set Antialiasing 16x.