I was trying out WindowsX Purist Firmware based in 1.1.6 kernel several hours, and I understand why some people like the stock version more.
It is simple, by the artificial extension of the bass and the "laid back" highs.
It is a more "easy" sound for many, especially for those who listen music with a lot of bass
But it lacks detail and the bas is deliberately exaggerated.
IMHO: It is true that the WindowsX firmware would have to be polished a bit, but as this it had much higher SQ than the stock firmware, so far.
I have tried it with a Hifiman 400i and also by line-out with an Accuphase C-265 with Focal SM9 Studio Monitors, this is where the best SQ is seen.