Actually this cable too doesn't have any type of certifications, and I don't think if there is any agency just to certify certain cables purity...perhap you want to start one...lol.
Anyways, I can only judge it with my ears. The sonic improvements are definitely, and jaw dropping. Especially the spaciousness of the IM04. Then the energy, it became more linear which further improve the soundstage, and then the tonality it became more transparency yet warmth but not as in stock form, the warmth in here is relaxing, tight, accurate bass in each beats. The bass is super accurate, punchy, meaty, clean. One thing to note though
Before the cables it sounds more realistic with it string and wind instruments, but the spaciousness in each band spectrum and specially in the MID + LOW was kind of compressed and too close together. I think this was what making it sounded warmer.
After the cables it sounds more Balanced Amatures. I said this before if you love Im03 in stock form, you will love Im04 with upgraded cables. I know I did as the 03 was so revealing that I had a hard time leaving mistake and errors in the recording, with 04 and the cables it still present, but less in your face and while still being revealing.
I was skeptical about cables before, but since ATH make this cables detatchable and then selling upgraded cables....there had to be a reason. I was just not ready to spend 200-250$ on another stock cables from them...so I went and seek down this cables.
I wish if there were more people with upgraded cable for 04 can speak up, as I don't want my impressions to turned into your disappointment. But as a headfier I want to share my experiences
****AlSO**** my plug is a balanced 3.5 TRRS. Could this be the uses of the plug and ZX2 hybrid balanced out ? Or the cables itself ? But a sure thing is that I "LOVE" them and the sonic improvement.
Again, the cables is stiff, but not that bad, and for what it trade off and the sonic improvements. It is worth it.