There was a thread a while back showing the waveforms out of the Z-controller. IIRC even with the knob at the full/max CW setting, the Z-controller output slightly "chops" the pure sinewave coming from the brick. I don't know if this is the explanation but the chopping surely can't help matters.
Would it be practical to insert a bypass switch. That is, even if the Z-controller did a true no-modification pass-thru of the brick voltage (when turned to full/max), this is still a step you must consciously perform to go into the DCS-RC "mode." Albeit another item in the chain, seems an electrical selector switch swap in and/or bypass the Z-controller when it is not needed.
