Apologies for the late answer.
In Windows, you need to configure the sound output to be stereo. You can do this by right-clicking the speaker icon at the bottom-right, selecting Playback Devices from the menu, right-click on your output device in this list (usually "Speakers"), and select "Configure Speakers". If you have stereo speakers, tell it you have stereo speakers.
Games depend on that setting to be correct. When a game starts, it looks at that setting and then uses that information to direct sound to your speakers. If a game supports surround sound but you have stereo speakers, as long as the Windows playback device setting is configured correctly for your speakers, the game will compensate for your speaker configuration and you won't miss out on any audio. The game will output all audio to your stereo speakers.