Disabling Onboard Sound without Editing BIOS Settings on Linux

If you are trying to direct sound to your external card and would like to disable onboard sound from your motherboard without editing the BIOS settings (for whatever reason), try the following procedure:

1. Run the command lsmod in the terminal and find the mods for your internal sound card
2. Next, run the command sudo gedit /etc/modprobe.d/blacklist in the terminal
3. For each module in the file, append "blacklist (module)" where (module) is the name of your sound module. Basically, we are telling the system to load the external card and not the onboard soundcard.
Here is an example:
# turn off internal soundcard
blacklist snd_intel8x0
blacklist snd_ac97_codec
blacklist snd_ac97_bus
4. Reboot.

If the above mentioned procedure does not work for you, alternatively you can try to force your external card to be the default one, via:

1. Run in the terminal: sudo gedit /etc/modprobe.d
2. Change the index for your external soundcard to 0 and switch the onboard sound to 1
For example:
options snd-emu10k1x index=0
options snd-intel8x0 index=1

In this case snd-emu10k1x (Audigy) is the external soundcard and now has been set to 0, and snd-intel8x0 (onboard) is the onboard sound and is now card 1. Of course the soundcard codes may be different in your case.