Simon, you can try modding your HLSC-1 with a small 4.7k resistor soldered into the common ground conductor of your HLSC.
open the 3.5mm miniplug by unscrewing:
mine has 2 red conductors: 1 for left and 1 for right channel.
and 1 common soldering point for ground - both groundconductors(l+r) are soldered to a common single point on the 3.5mm plug“s shaft(ground).
get soldering equipment and do it

. you can easily undo the mod aswell.