Probably a bit optimistic thinking about the 2x, while technically possible, I think I recall the image quality was not great and you'd be well into diffraction. The 1.4x might be more feasible - AND if you don't have a switch on the port to activate 2 x you could use the converter to get more magnification.
It sounds like Nauticam are taking the approach that a CMC-1 is a better solution than activating the switch? Though I would think for many purposes a lower power diopter would be a better option. Advertising 3.5x sounds great but that is an imaging area 5 x 3.7 mm where you could fit a grain of rice and not much more.
Then there is the working distance........ 15mm at 3.5x! not particularly usable and even the CMC-2 is 25mm at min focus.
It's all on the port chart now though curiously the chart says the setups are designed for the switch to be set at S- macro - I would suggest that publishing figures for the CMC lenses with the Switch NOT set to S- macro would be more useful, even the CMC-2 achieves 2.9x and finding subjects that are interesting beyond the fact that they are small will be a significant challenge, never mind the shooting challenge of holding back and forth sway to less than 10% say of the depth of field of 1mm or less. Using the CMC lenses without the S macro switch would give similar results to the Sony 90mm macro for magnification. Here's the port chart:
https://drive.google.com/file/d/1sCwkAl718plkFf7wjg0wKadyBZtfN25p/view