ok, follow these instructions:
The neufbox is the closest model to the SFR that I can find.
On this page are instructions for port forwarding for your router.
Follow the instructions from Step 3 onwards.
In your router click on:
Reseau, NAT
In the fields immediately underneath
NOM = Soulseek (this is just a name reference for you, nothing more)
Protocole = TCP
Ports Externe = 56805
Adresse IP de destination = 85.168.17.1
Ports de destination = 56805
Activation = tick/check in the box
Click ADD (red button)
Now go to Soulseek client, and recheck TCP open/close.
If you get to this stage, write back to this thread.