Since the Etherwave Pro seems to have gone through some factory modifications to its volume control circuits during the short time it was in production, could it be that the famous Thierry magical module only works on earlier models?
I was very pleased with my magical module, but my E'Pro was from the first generation.
If Etherspiel's volume field has contracted since he installed the module, it could be that the tiny inside screw whose access hole can be found just next to the ports where the loop plugs into the cabinet, needs to be adjusted. This screw is for gross adjustment of the volume field and the slightest change, even one degree, in its setting can make a HUGE difference.
It has been my experience (and I've had PLENTY, believe me!) that whenever you make any sort of modification to a theremin the entire instrument can be affected in a variety of unexpected, and sometimes inexplicable, ways. There's a kind of "domino effect" that happens. This can necessitate all sorts of adjustments to parts of the instrument that have nothing to do with the area you modified.
Etherspiel, you may have given up on the magical module prematurely. BTW I have enjoyed your intelligent and informed posts to the "Levnet" section of this forum more than I can tell you!