I will try to explain it different way:
1) Sonar has mapped (all) controls of Mackie Control Universal device to perform something useful in Sonar. Many labels for buttons on that device have no sense in Sonar, so labels had to be changed by an overlay. The same was in other DAWs since original device was labeled for one particular DAW, and that DAW was not Sonar
2) X-Touch is a clone of Mackie Control, the same controls which send the same signals and have the same labels. So it works exactly the same as it was thought originally (ALL controls), but an overlay is also required (to label buttons correctly for Sonar).
3) the plug-in for Sonar was not significantly changed since it was written for very old Sonar version. So in new Sonar one specific set of functions, working with ProChannel, is no longer working with Mackie devices (and so with any clone) correctly. That can be solved by mod (free to use, public and open source). But mod is not covering the functionality not foreseen in the original plug-ins, controlling extra ProChannel modules and SoftSynth. That functionality is theoretically possible using completely different plug-in (free to use, public but not open source).
4) FaderPort8 has insufficient number of (hardware) controls to completely emulate Mackie Control. X-Touch has all possible controls.
Note that X-Touch is a clone in functionality only. It is build from different (obviously cheap) components compare to the original Mackie Control (Universal/Pro).