Generally you can enable it in game. For DX11, MSAA sure as crap isn't the best looking at all, it basically does nothing other than drag the framerate to its knees. Sadly this affects most AA options for Nvidia in DX11, you'll pretty much have to experiment game by game, or just go without it. MSAA also does nothing on transparent textures, so if the game you are playing has alot of trees/bushes/grass etc it won't help much. There really isn't one blanket AA you can use on all games. Only method you can universalize is downsampling, works in all games and undoubtedly looks the best, but the performance hit is pretty big.
Also, the Nvidia Control Panel likes to lie to you, it will say it has activated AA, when alot of the time it simply ignores your custom profile, this is to stop people activating an AA type for a game that might possibly not support it, or have some issues when it is active. To get around this, you have to use Nvidia Inspector to remove the flags that stop it from doing so, the option is something like 'Treat override as application controlled', you just change that to 'None'.