This video is belonging to Porta.Fi, you also can check his Youtube channel and subscribe it. He is very professional on reviewing this.
Fiio M11 or Fiio x7 II?
When it comes to usability M11 is just better, it handles harder loads much faster (Faster SoC, bigger RAM), Overall it is a hassle free experience.
X7 Mk2 in the stock form will not sound better than M11, stock amp module of X7 Mk2 is weak and has just a bit of hiss with IEMs.
M11 internal amp is noise-less, even with very sensitive IEMs.
However, you can make X7 MK2 sound better than M11, that is true, only by using a better amp module like AM3B or AM3D, but it adds to the cost.
M11 is a 450 USD device, X7 Mk2 is 650 USD + add another 150 USD for AM3D and you have almost doubled the price.
If you have the cash and if you care only about SQ, X7 Mk2 might be for you. But, I would advice against X7 Mk2 at this point as its successor is around the corner – a little birdie told me it should be released later this year.