I tried to measure my right and left channel voltage now with the suggestion to use my UE TF10 cables. I currently can only use a cheap chiense meter (which cant sit still .. wild jumping numbers until you actually measure something, then it stays stable .. a battery I tested etc, so the readings seem ok). I played music through the topping asio driver and had the dx3 at around -12 dB on the USB port.
On the left channel I was measureing voltages around 0.3V +- 0.2 while music was playing .. it did that for as long as I would measure.
On the right channel, whenever I would connect my probes, it jumps to 5 or 6V and then fell down to 0.
In the attached video I tried to show that. The first half is the right channel .. the numbers show Volts. You can see how it jumps to 5 or 6 when I touch the cable pins (the random numbers before are just my device...) and then it falls to 0 .. then again to 5 or 6 .. then 0 again. The second half of the video shows the left channel ... normally playing I assume.
Video: