A demo on configuring your distribution to use your new audio card can be viewed at (demo'd with Ubuntu 18.04):
* Despite the excellent sound card demo'd the video was not produced with the sound card nor a proper microphone
http://www.freedomdecrypted.com/public_html/demos/sound-card-video.webm
Depending on the version of Ubuntu, Linux Mint, or Debian you are running you may need to install the alsa-utils package. If you need assistance on another distribution please contact support.
0. Before you do that make sure your speakers are connected to the green front audio output jack on the sound card and your speakers are powered, on, and the volume is up sufficiently!
1. To install the alsa-utils package open a terminal and type:
sudo apt-get install alsa-utils
2. If prompted for permission to install use your Y key on your keyboard to say yes.
3. Now run alsamixer by typing the following command and hitting enter:
alsamixer
4. Hit the F6 key and select your sound card (Xonar DGX)
5. Use your right arrow key to get over to "Analog Output" and arrow up/down to change to "Multichannel"
6. From your graphical audio applet you will also need to make sure that the sound card is selected: Analog Output - CMI8788 [Oxygen HD Audio[(CMI8786(Xonar DGX))
7. You can also test your sound using the test speakers button here.
8. If you still don't hear anything make sure the output volume is not muted. If you get sound using the Test Sound feature make sure the application's audio volume is also up loud enough to hear it.