You should go into the set up menus for the receiver and the source unit where you will find locations to assign the output/input to the optical out/in. This should be described in your owner's manual.
As Jan says, with many receivers, you need to tell the receiver that for example the DVD input should expect a digital input from 'Opt 1'. You usually do this from the setup menu where there is an Audio assignment menu. It should be in the manual too.
Eduardo, this the 4th time you have posted on this issue. Consulting the manual has been stated time and again. I posted the CES connections manual for you.