Built in audio output (speakers) are playing through different channels.

My built in audio output (speakers) are playing through different channels. How do I make them both play through the same channel? It has something to do with the audio midi setup. When i click "Configure Speakers" on th Built-In Output I don't get the option of "-" for which channel the audio should go out of, I just get "1" or "2" as an option. This happens when i select them to be both stero and multichannel speakers. Any ideas on how to fix it?