Well my guess is they use Multicast. Then you would need to find a way to have L2 level multicast on the repeater. Did you use WDS to make the repeater? Or can you look at Mesh?
If all that not working then need to look at proxy solution
Orange TV certainly requires a VLAN and/or a NAT. It it supposed to be used directely connected on the Livebox. The official orange repeater surely has built-in tweaks that you are not aware of.
You'll need technical informations. I have this scheme from a previous thread: it may use VLAN100
Orange modem/router (box) are known to be poor on features, and a real pain to configure. Many features or configs and not well documented (who said "on purpose" ?).