It seems odd that the initial creation of SubD objects is so basic, especially as in other Autodesk software it seems more intuitive? So in Alias when you create a SubD it appears with no interactive manipulator, you have to turn on its controls before manipulation, and type in values for the spans in a dialogue box ( and you cant link the fields so you have to type in XYZ separately). Please make SubDs appear with controls on by default, and add a manipulator that allows a simple mouse drag to increase or decrease spans in any particular direction, or all directions together ( as in other software), or perhaps you are already doing this?
Regards Brian