after few calls to some friends musicians I finally understood how things work , on TOS LINK .
Tos Link DOES support the codec dolby 5.1 .
So for example if you download a movie from http://www.apple.com/trailers/wb/oceans13/hd/ wich is dolby 5.1 you will be able to use the tos link to transport the TWO digital audio channels with a 5.1 enconding to a de coder to get the 5.1
But if you want to use the DISCRETE output , wich it mean no encoding , you CAN'T use the TOS LINK .
TOS LINK can only be used for TWO channels , and if those TWO channels are encodec with 5,1 well it support it .
What's it's important is that Catalyst-PM can play both Dolby 5.1 and up to 24 discrete output .
Note to get 24 discrete output you will need a multy channel audio card .