How are you coming along with the build? I have the same machine and doing retro now. I have everything from CNC4PC as far as control goes. DGS4 16035 drives and HEDS 5500 A06 encoders with the same motors. My transformer is different as it is 220v and I have a 10a variac tuned to 63v out after the caps. I looked into getting new toroidal transformer but my engineer said why? It is messier for sure but oh well. It has it's own separate enclosure.
On my HEDs PDF it says supports resolutions to 1024. I have the control set to 1000 and it is moving just fine and tuned well as far as "/rev. My PDF doesn't say 500 anywhere.
https://youtu.be/7YHo-DRnSKY