Flashcut and your signal generator (SG) should be able to run any motor driver out there. Is your SG one such that has the 4 drives right inside the SG box and a wall transformer ?, Or, do you have a second box with a power supply and drivers in it ?
If your drivers are internal to the SG, you should be able to pull those drivers out. There might be some slip-pin changes to make if you do so.
Once your back to having just a plain SG, you dont need to really buy any "kit" or breakout anything to make it work. Just make a new cable with a DB25 on the end that plugs into the SG, and the other to the appropriate locations on your drivers. All of Flashcuts pin configurations are WELL detailed in their manuals.
If you dont want to make up an entirely new cable, you can find a premade DB25 cable, one that has all the wires, and put a breakout board on the other end for easy connections.
Depending on exactly what you have there, You might be able to use the drivers that still work and just toss in a new one for the bad one, even if its a different brand.
One last question,... if you have 4 axis drivers, do you need all 4 for your shopbot ? Does it have 3 motors or 4 to drive ?
If we can hook up via regular email, I can send you some connection diagrams typical to Flashcut that will make things much clearer for you.