I don't really understand the question.
Mod wheel is connected through various way, depending on the presets.
Modulation section : the source drop down menu allows to choose the Mod Wheel. The destination drop down menu allows to choose Osc1 pitch (or Osc1 and Osc2 , or Osc1, Osc2 and Filter).
The Joy stick : on the right side of the joy stick you can see three double sliders. The first is to set the Joy stick LFO frequency. The second is to set the amount of the pitch bend (connected to the vertical movement of the joy stick) apply to the oscillators (1 and 2) or the filter. And finally, the third is to set the amount of the horizontal movement of the joy stick apply to the oscillators (1 and 2) or the filter.
If the little leds labelled "WHEEL" are engaged, then the modulation wheel is connected to the vertical movement.
So depending on the presets, if you want to remove the modwheel connection, you have to remove them manually.
Is there a global way, not to send Mod Wheel information to the Synthix ? No, but if a lot of the users are needing it, this could be done.