I have changed the cable of a Hifiman Edition Xs and I notice the cleaner sound.
I bought an 8-core 4.4mm cable to take advantage of the more power output but a 3.5mm cable came to me…I was disappointed but gave it a try…
I have put it in the Edition Xs and I feel like its sound is clearer. The difference is not day and night but it exists by doing A/B tests.
I’m going crazy?
Hifiman stock cables are notoriously shitty and they measure poorly as well so, no you’re likely not going crazy. When people say they don’t hear a difference between cables they mean between two cables of good quality with different conductive materials and such. By getting and 8 core cable you’ve simply gotten a good quality cable that’s better than the dental floss that comes with your average Hifiman lol! 
The issue of cables is very controversial, isn’t it? I see cables for more than 200€.
I didn’t know hifiman didn’t make decent cables. Especially for the Edition Xs which is already worth over 500€.
What should I look for when buying a good cable? The cores? Purity (5N/6N/7N)? Oxygen?
The concept of different core materials causing a difference in sound is certainly a divisive one. You’re right about that. As for looking for good cables, ideally you would measure the cables you get to make sure they have very low resistance. That said, generally you’ll get good performance from any cable that has adequate cross secctional area to transmit the signal and that used decent terminations that are soldered and assembled well. Thankfully, nowadays you can find cables with thick cores or higher counts of thinner cores that have good conductive properties andow resistance for quite cheap.
Hifiman has updated their cables on some models, but they are still known to be adequate at best, even for their higher models. They’re well known for including thin cables that aren’t well made and that measure very poorly.
With how popular it has become to grab premium aftermarket cables there really isn’t any excuse for it either. I personally don’t find that I hear a difference when I purchase some multi-hundred dollar silver and unobtainium monstrosity with depleted uranium connectors to when I purchase a quality 8 or 16 core occ cable of regular quality. Sometimes I’ll purchase some really cool or exotic cable just because I dig how it looks, but these days I believe you can find all the performance that you need in the sub-$30 bracket.
it could just be the better balanced out most amps have bringing more out of them.
some people do say there is a difference between silver and copper cables but as always different ears and setups lead to different results.
Good point. If his amp has a better balanced implementation than SE it could indeed sound better.
I don’t know because I’m not you, but I will say that assuming you’re plugging both into the same output on the same rig and using them with the same headphones I wouldn’t expect to.
Some say that balanced outputs are usually few dB louder than 3.5 mm outputs with the same knob position.
They should be. Balanced outputs generally have roughly twice the amplification power as single ended.
think for most HP its enough to get some decent OFC cables with quality connectors or get some mogami or sommer cable microphone wire and do it yourself 
only for totl HP i would spend money on community recommendet cables and only if the rest of your chain is also there ^^