Hi Charles,
It seems like KFLOP/Kanalog may be a good candidate. But you would need differential encoder feedback. Not sure what your AXS or RLV boards might be. 8 encoder wires wires would be expected for +5V, GND, A+ A- B+ B- Z+ Z-. If it has Resolvers instead of encoders I'd suggest changing to encoders.
You can add up to 192 additional optically isolated 24V IO by adding one or more Konnect Boards.