I upgraded an old 12v Routout CNC 3 axis box to 4 axis around 10 years ago, the signals are there to run other stepper drivers but after experimenting with some cheap drivers I was lucky enough to get the last new old stock matching board from Routout CNC.
If I found myself in the same situation again I would use a modern buffered breakout board (the Routout CNC breakout board provides no electrical protection either way) an decent drivers as the cost would not amount to much and the results would be far better than the original, the original box is still working for the gentleman who bought my desktop mill around 5 years ago but even he has seen the shortcomings of the low power output and is upgrading to a modern self-build box.