cheers Greg F,
I've got to admit a deficiency, I never learnt basic electrics - how to solder, or even use meters - depite playing for 40 years.

I really should do some youtube tutorials..

So, do you all concur with Greg's diagnosis, or have further ideas ?
I'll be phoning the cable brands product support again sometime soon.
so need to be properly informed and prepared.

I'll tell you why this is of greater interest to me.
Presently I own a few hundred pounds worth of power attenuators for connecting between valve amp heads and speakers.
This helps give fairly ok power valve tone at much reduced volume levels.

Not the most convenient set up for simple quick n easy home practice.

I can plug an overdrive / clean boost / etc FX pedal into a small combo amp
- push the amp vol up, while keeping the pedal output very low.
Buit it's not ideal.

So the idea of a properly tweaked product like an effective inexpensive 'attenuator' guitar cable - if it could exist in practice -
is actually quite apealing.