Possible retrofit of a Körner Magic550 CNC Machine

Hello everyone.This is my first message here. I’m trying to gather information about a machine that we have at work and that my boss wants to retrofit. I suggested Linuxcnc and Mesa and as I suggested it I got the job of finding more information.
The machine in question is a German machine made in 2005 by the Körner company and the model is Magic 550. It’s a 3 axis machine with a fourth servo for the toolchanger. The servo drives are unmarked and so are the motors. There is a windows XP running PC which has a Serial pci board with 8 serial ports. From this board there are 5 RJ11 cables going to the servo drives and to a breaoutboard which is located separate from the drives. We have some schematics in which the XYZ servos are labeled as Haidenhein and the tool changer servo is labeled as Siemens but there is no label for the drives. The software which runs the machine is called CNC900W. 
My question is ,can someone help with figuring out what signal type these servo drives accept and recommending the appropriate Mesa card.

Ok,thanks for replying. I managed to take some photos.

More info. I found a brochure online where it says that the software controls the servos digitally and something about frequency  16khz and 14bit so I think it’s safe to say these are not analog controlled.
On the schematics the servos are listed as QSY96G for Z axis ,QSY116J for X and Y axis which are from Haidenhein and FK7022 for the toolchanger which is from Siemens. I looked online for the recommended drives for these motors but they don’t look like the ones that are in the electrical cabinet .

Ok,that’s not good news. Can you explain a little how serial interfacing might work ?
On the other hand I searched about the recommended drives from Heidenhain and they are PWM controlled. Can Mesa cards send PWM signals?

Not much information on the Heidenhain drives.  Can anyone recommend a alternative servo+drive combo to the motors that are now in the machine. I have attached all the info I have found.

I attached the link to the manual for the Heidenhain servo drives which are compatible with the QSY motors that are installed in the machine . Maybe someone can shed some light on how these communicate with the pc. UM310 is the drive that is of interest . 

www.heidenhain.it/fileadmin/pdf/de/01_Pr...OEM_ID1303180_de.pdf