Nobody does, and at this point it will be just a speculation
There are so many budget and high end daps that share the same dac chipset, yet have night and day sound. Of course, implementation is important, power filtering is a big deal, isolation of digital and analog domains to keep noise from coupling in is important, but in my opinion the amp section of the design is a huge deal in shaping the final signature.
I know x5iii keeps coming up in the discussion and I think many consider it as one of the contenders for comparison, but I don't see it like that at all. Maybe when you relate features due to running on open android platform, but it has been mentioned by both fiio developers and testers (ClieOS) that x5iii is still has a mid fi sound and not in the same class as x7. So if anything, a proper comparison will be to x7 or the upcoming x7ii.