Brian.
OK for what it's worth, first try to get the machine with the ROD426 encoders working first. These are 250 line differential output encoders and will work fine with either Gecko G320 servo drives ($114 each) or the CNC Teknix TEK10 Drive ($324 AUD) The gecko's will work just fine and there's probably no need to have the extra sophistication of the TEK drives.
These will all work out of the box with Mach3.
The encoders will need their own 5v power supply as the Heidenhain encoders have a faily high current requiremnet. I have the pinouts for these if you ned it.
Do you have a pic of these machines, it's not a machine I have seen I think.
Wayne....