Don't jump into a conclusion about cables yet
No matter how great they sound paired up with one set of IEMs/CIEMs, it doesn't guarantee the same synergy with another one. I found pure copper cables to smooth sound and to improve low end impact, with some IEMs. Unfortunately, a lot of my aftermarket cables have mmcx connectors so I can't test it with Ei.xx, but I have a feeling that pure copper might not be a good match for Ei.xx because you are going to shift sound more toward a darker low end side. I could be wrong and this is a pure speculation, but IMHO I think Ei.xx will benefit more from cables with silver in it to brighten up a sound, giving a little more edge instead of "smoothing" out that edge.