Its never gonna happen that i pay for MMCX to IE800. Huge waste of money since i dont believe in cables. Never heard any difference. Either when playing instruments or with speakers/headphone/IEM's.. When i did electro and electronic at school, the cable question came up regularly and we learned that its mostly snake oil. So that is what i think. But a good quality cable is important. For durability/flexibility.
Thats what i think though. But i also mean its important to respect other peoples meaning It would be cool(or more expensive) if i could hear difference with cables for tweakabilty etc. But i just dont.
I think you are reducing the cable swapping to attempts to improve sound quality. It may or may not be there, I have my own opinion on it.
But consider that most people change cables for improved ergonomics, fit, best use for their setup. I have aftermarket cables on all of my Sennheiser overears because I wanted a different length and different feel to the cable. If I use my overear headphones 95% of the time at my workstation, I don't need a 3m cable, it gets in the way. And if I use it 8 hours per day, I can choose to pay much more than the price of the stock cable to have a more suited sleeve rubbing against my workshirt all day. I may even get a small enjoyment out of plugging in a full metal Furutech 6.3mm connector compared to the flimsy stock cable that has a bit of a bend to it from the box.
What I am trying to say, cables are about much more than just changed acoustics.
Now, I personally like the cable on the 800S, less so on the 800. But I would only change them to MMX if they broke in the distant future. As it is, they work for me as overears (but almost at the limit) and the thinness of the current connection to the earbud is an advantage for me. I can see how someone would need to adapt them to MMX just if they can't get the overear to work because of the length of the stock cable. I like the feeling of the cable coming together just under my chin, someone else might hate it. Conversely, I did not like the look of the 800s after MMX conversion (based on a picture here), someone else might love it.