The problem was due to the cables between freebox and slingbox. For those who could face the same issue with the freebox, here is the workout I found (probably not the most efficient but it is working):
A s-video cable
A mix of peritel cables
I had to use cables not provided with the slingbox and I an sure there is an other way to do. However, it is working :-)
I am trying to connect the Slingbox Solo to Freebox V5. What additional cables did you need? From your picture I can see that you are connected to your Freebox V5 by S-video but I am not sure I understand how you connected the audio with the cables that Sling provide. Can you please explain?
Wish your pictures did more justice to your excellent solution.
Sorry if my solution in the attached pdf are half French and half in English but if you are gonna be watching Freebox then you should know French and if you are reading this post then obviously the rest is easy. Hope this helps sort you the connections to the slingbox.
Slingbox Freebox connections.pdf 556.6 K