But now the thought that has me excited, based on that voltage divider crosstalk math above, is: what if we remove the common GND wire from the cable and have the return wires from the cups join up as late as possible, i.e. at the GND terminal of the plug that goes into the amp? Well, that would move the common ground wire’s resistance from the common part to the driver part of the equation, making the crosstalk 20*lg( 0.1 / (0.1 + 18.1) ) = -45 dB!
That would be over 15 dB of improvement in the crosstalk, just from switching to a pseudo-balanced cable that has 4 wires for its entire length but terminates them with a TRS plug at the amp end (R- and L- both connect to the GND sleeve of the plug). You’d just change the cable and keep the SE amp you have, no need to buy balanced to get a big improvement in stereo separation. I definitely have to try this for my Verums after I get them, because that 1.8 ohm cable vs. the 8 ohm driver will not be doing me any favors on the crosstalk side.