Hi,
OpenGL has antialiasing controls which the application can set, but due to an architectural difference between Windows and X11 we cannot change the multisampling settings. Luckily it is still possible to enable it in nvidia-settings like you did. Are you sure you activated it properly? Can you make sure to enable anisotropic filters too? Those should be activateable in the game, as well as in nvidia-settings.
Crossover 6.2 in theory supports -dxlevel 90 in half life 2, except of sRGB writing, and it is unplayably slow thanks to sRGB texture reading. So support for sm 2.0 and 3.0 is deactivated by default, and HL2 always uses dxlevel 81 max. I have implemented sRGB writing already, and I hope to fix the sRGB reading performance problem and enable dxlevel 90 by default in 7.0, including high dynamic range rendering. No binding promises given however, my issue list is very long still 😊