So are you saying that your speaker cables are plugged into the HF posts? If so, the jumpers aren't in the signal path for the part ot the speaker than makes 90% of the "color".
Sound color with different jumper materials,
Change the sound color with different jumper materials, have you ever tried using solid core copper silver vs multi strand gauge, to see if the high frequencies improve? Currently my speaker wires are plugged into the HF with the multi-strand jumper and gauge going to the LF. Have you ever tried connecting the speaker wires to the LF terminals and using a solid core copper/silver jumper to the HF. What were your results?