I'm a mechanical guy, but my two years of computer science courses are telling me that it shouldn't be difficult to just make them appear to be one speed controller in software, especially if you are using C++ or Java.
You probably wouldn't want to put them through one speed controller anyways. The maximum current you are allowed to supply to a speed controller is 40A. If the two FP's were drawing 20A each, you would get about 0.25Nm of torque. If each FP was drawing 40A, you'd get 0.50Nm. Keep in mind that an FP stalls at 70A, and 0.45Nm.
Also, my team is using a winch, driven by a CIM and an FP geared to the same speed as a CIM, and there is no PID loop, and since we are using a CAN bus instead of PWM, we didn't use a Y-cable. We're simply telling them to turn at the same time, same speed, and same direction. Seems to be working fine
