usual norm is the lower output impedance, the better. it is exceptional when a manufacturer recommend certain higher impedance, in order to reduce hissing, or in order to alter highs frequencies. for the first case, special impedance adapters which don't increase total output impedance are recommended. for the second case, i'd prefer a better original tuning rather than modifying it with output impedance. we know some cases: er3xr with impedance adapter, reduces noise/hiss and increase highs level, so it looks like near er4xr tuning (see clavinetjunkie video). the effect on kz zs6/zs5v2 is the opposite, higher output impedance tame highs levels. it depends of the impedance of the iem (balanced armatures impedance and crossover). in general, it's a bad idea to do this. if you want to alter frequency response of an iem, you'll get quite better control of the result by equalizing. blessing is not an special case like these. i'm using xduoo x20 to test. its output impedance is 0.12Ω(single end) / 1Ω (balanced). in single end, i shouldn't notice tonal difference in blessing between 0.12+0.06(cable 125)=0.18Ω and 0.12+0.20(cable 165)=0.32Ω. it stays very low. in balanced mode, 1.06Ω vs 1.20Ω, not much difference either. so i'm going to sacrifice a bit of output impedance in order to get the darker background and better definition from the 7n up-occ wire. of course, i'd prefer lower cable resistance, that's why i asked for 8 cores version of these cables (near half resistance).