Running Multiple Channels of Audio Simultaneously in Linux
In Windows, I configure my Realtek audio to play sounds through my headphones (plugged into the front panel jacks) and my speakers (plugged into the rear panel jacks) simultaneously. I noticed in Ubuntu, the default is to mute sound in the rear when a device is plugged into the front. I wanted to stop this behavior, so here's what you have to do. Some people may also be looking to mute the rear speakers when a device is plugged into the front, so I have included both configurations. Download this nifty utility to manage and configure your audio settings by running these commands.
sudo apt-get install gnome-alsamixer alsamixer
In this application, you can adjust volume and mess with several other settings.
At the bottom of alsamixer, scroll over to the "<Auto-Mute>" option.
To play audio through both headphones and speakers, change Auto-Mute to "Disabled".
To play audio through only one device, change Auto-Mute to "Enabled".
Hope that helps!