This is all determined by Windows Audio settings. If you have set a 5.1 audio environment, and are only playing using stereo or 2.1 setup, you will be missing out on many channels of audio. The simple fix is to match your current speaker setup with what windows expects your audio configuration to be.
If you have 5.1, tell windows 5.1.
If you have stereo, tell windows stereo.
If you misconfiguration these settings, you will be missing out on audio detail.
If you can't hear audio (dialog) in your game, you are probably misconfigured.