In order to properly configure your audio card to output on 5.1 audio channels, you first need to download and install the latest driver that is available for your audio card. This can be found on the official website of the manufacturer. After you did this, depending on the OS that you are using, you can go to Start > Control Panel > Sound > select the speaker and press Configure. Select the audio channels 5.1, test them and follow the instruction provided. This should solve your problem.