Sercos 3 (iii) with Linuxcnc?

I've just purchased a 2008 Weeke Vantage 33 cnc router from scrap. The machine is in good condition and I'm going to convert the controller to lcnc.
The servos are Rexroth Indradrive and as best as I can tell they're using sercos iii. My drives have a fiber ring connection rather than Ethernet but the logo definitely says sercos iii. Apparently there were some iii drives made with fiber connections. 
The io is all Beckhoff and the pci card in the pc is beckhoff also. 
Is there any workable, straight forward way of controlling these drives using lcnc and, perhaps, the beckhoff pci card? 
If so then great, much better to use the hardware as is. 
If not then I'll go down the path of selling the rexroth drives and motors and buying Delta or something along those lines. 
Any info of advice greatly appreciated.
Cheers

Hi
i just ran into your post about the DKC drives
Did you manage to solve your problem with the sercos protocol or did you replace the driveline?
I am in the process of retrofitting a bof411 Homag with the same driveline as yours and  Ihave successfully modified the DKC drives so they now run analog by replacing the firmware
Feel free to reach out if interested.

 

How did you manage to replace the firmware? Did you replace the sercos-bus modules in the drives or are there analog inputs in the drives already?