By far the easiest way to do this is to enable the DSR resolution option in the NVIDIA Control Panel. Speaking of which, I've found that by far the best way to improve the visual quality of the game is to up the resolution. (Or if you for some reason play AoW III on a big screen TV across the room and the text is hard to read on the normal size UI) Autoscale UI should be off at 1080p, it is intended for playing at higher resolutions.
I always have the SSAO option on for the little extra 'depth' it adds on the shadows.
AoW III's anti aliasing option (an old sort of FXAA) definitely contributes to the 'blurry' feel, especially when your map is zoomed out a bit, and I never enable it personally.