Well, unfortunately I did not get the right cable, they sent the one with an 'ear guide' even if the product images looks like it's straight. I can't pinpoint any polarity issue in the sound, tried the connection in reverse also. Polarity seems correct when connected the correct way with the ear guide pointing the right way. Unfortunately though, there is a big sound differense compared to original cable, original is much better. There is a huge boost in the 6khz range with the new cable, making them very sibilant and piercing, they were not before. You can fix this with some EQ, I had to lower 6khz by quite alot: -7. The amazing thing with FLC8n was that they didn't ever need any EQing, so this is a clear proof for me that cable affects sound.. alot in this case. Reversing polarity didn't fix this.
Is there a conclusion, well, not sure. Next time I buy a cable for the FLC8n im not gonna buy this model at all, even if the connector would be correct due to the heavy 6khz boost sibilance.
I bought from this store, so don't buy from them.
https://www.aliexpress.com/item/4001042333305.html?spm=a2g0s.9042311.0.0.66b14c4dfYxpUT
In any case, here is something I am sure of. The connector should look like in image 'correct', make sure the connector in the product images looks like that
Also the transparent connector looks pretty ugly with the blue flc8n, suggest black colored connector
Still, this cable I got is better than nothing of course. Got half the cost back from aliexpress due to the misleading product images.