[MetalMan]

Another reason why using 2 controllers on 1 motor might not be a good idea would be because all controllers are not made 100% equal (as in there are variances, as noticed between 9918 controllers with brake fade). The controllers could be fighting with each other due to their differences, causing extra stress (and possibly smoke!). The basic thing to do to get a more powerful controller would be to add more FETs on. Paralleling 2 controllers almost does this, but there is still the other circuitry that could cause problems.