A new moving coil is a big deal, far more so than a cable. Lower distortion has been pointed to as a factor in microdetail/ clarity a.k.a. "plankton".I'm glad to hear about a mkii, I think I may well pick one of these up.
There have been many, many studies on the effects of cables on audio performance. They almost always show no difference. That's not to say that settles anything and there is a Sound Science forum for cable debates, I'm only pointing out that there is very, very, very little data to back up claims of cables making any difference in sound quality. If you can find a study that shows a difference there will be 50 that don't. People do hear what they hear, of course. Just...
Unfortunately, I can't see anyone buying this earphone with the QC track record it has. It's not just one batch, but pretty much all of them that have this problem, it seems. Too bad, they were on my purchase list.
I'd love to talk to someone from Beyerdynamic to get the real picture on these. Like has happened with some other lemon earphones, these will likely be discontinued by the end of the year. Just a guess, depending on backstock.
In general, I'd recommend using tips that seal quite well, but with no feeling of suction (which prevents the driver and also one's eardrum from moving properly). Whichever tips do that are the right ones, the seal is more important than the tip used. You could try the jvc spiral dot tips, as they are popular, for example (assuming they fit, which one of the tk8ie owners can confirm).
Sounds like you haven't studied the difference between dynamic drivers (ie800, speakers) made for music versus balanced armatures (multi-drivers made originally for hearing aids. Entirely different technology is how a single dynamic driver can beat multi balanced armatures.