Pulseaudio is the audio system which will be used by Ubuntu. You can go to hardware settings tab and select the output type for your system.[choose Surround or digital output] Here, you cannot change the output mode. To change the output mode, we will make use of PulseAudio equalizer.
Newer version of Ubuntu's will have Pulseaudio installed. If it is not installed, then go to terminal and type
sudo apt-get update
sudo apt-get install pulseaudio
To get equalizer, first download pulseaudio equalizer from here.
Download
Now go to Applications->Sound and Video->PulseAudio Equalizer.
Here you can see the snapshot of pulseaudio equalizer :)
You can select the mode of output and save presets :)
Enjoy with better quality sound from now on :)
Thank you for reading this article :)