Impedance difference effect sound in all drivers. DD actually more. The bass has much more range to change then say if you put an Ety P to S on the Ety it will sound a bit more tighter and quicker and accurate but not huge. Put that on some dynamics and there is much more audible bass difference(always a lessening). The BGVP A/B/C tuning adapters are built for that as well. I can put the "A" reference cable on many a dynamic and the bass will really drop. Harder to drive usually leans the bass in a dynamic provided it is enough impedance added. Zero surprise to me esp. since it sounds like it adds enough. Doubt there is anything wrong with the cable. Some cable are about propagation speed and being easy to drive others are about adding resistance. Like Linum cables can be 2.0 ohm or 1.5 ohm or .75 ohm. They recommend if you want more bass go to one of their lower Ohm cables.