With Fanvil you have to have the correct number of buttons. x6 has to have a definition of all 12 buttons. A x4 has to have 6 12 18 or 24 buttons defined.
I have done a lot of mods to our fusion to make provisioning for Fanvil's work for us. we have x4 x5s x6 all working. I'm working on the x210 at the moment.