It is possible that you only replace the EZCAD2 LMC controller with the DLC controller to use EZCAD3. But it requires many changes to your current machines. In our experience, it is really complicated and there are many failure cases.
And in terms of cost-effectiveness, a single DLC controller plus EZCAD3 costs at least 1300USD (shipping cost included).
It is more suggested to buy the upgrade kit.