1. Can't comment.
2. It depends on the point of reference from which it's being described. Coming from HD800s, sure it is darker, but there are darker phones. I do not believe anyone can tell you if it's dark or not since that depends on what your ears are used to ("neutral" is also subjective). However, to me, they sound pretty natural, nothing that tells me they are dark or bright.
3. They excel with many genres, but I prefer Audezes for their exceptional performance with jazz, vocals, piano, and rock.
4. This is entirely subjective since some have better ability to hear than others. I can hear differences among cables, but I can't tell you if they are actually improvements or not. My ears found some cables more favourable than others, but that's as far as I can go before kiddies come at me with torches. The only way you'll find an actual answer to this question is to try cables yourself. Do note that while many kiddies say it's all placebo if you do hear something, remember that if it works for your brain, it is working**.
** If a sugar pill cured a headache due to placebo, you cannot say the headache was not cured. It was cured. Don't be an idiot.