Turn off S/PDIF digital audio in Ubuntu installed on Mac computers

My Ubuntu running Mac mini got the S/PDIF light always on, like this:

To deactivate it start by running this in the terminal:

sudo alsamixer

Move to S/PDIF with the arrow keys:

Then press M to mute.

Press escape to exit and without closing the terminal run:

sudo alsactl store

To make this permanent on every boot go to Startup Applications under the System Tools -> Preferences menu and add a new one with this info:

Name: Restore Alsa State
Command: /sbin/alsactl restore
Comment: Turn off Optical Out

The same command (/sbin/alsactl restore) could be added to /etc/profile instead.

To only deactivate it temporarily you can just run:

amixer set IEC958 off

Ref: https://help.ubuntu.com/community/MacBookPro7-1/Maverick#Sound