Cannot play Half Life in 5.1 using ASUS Xonar Xense

Right now I am using the ASUS Xonar Xense Audio cards. I found them as the first class audio cards for Desktop computers because you have different choice to choose from them depending on your needs and I think that all of them come with quality headphones also. The problem while playing the team fortress and Half Life 1 game, I can only get stereo mode with this sound card. There is no way I can set to 5.1. I would like to play games like this in 5.1. I tried the GX emulator and it seems that that does not effect at all. However the modern games which are recently released work perfectly in 5.1. Then what could be the problem with older games. Should I need to install any patch or mods for games?

You should see game website, half life is very old game now and I don't see any patch coming soon specially for your kind of card because not everyone us it, neither its very famous one.