I have MX-R and KX-R in my system, in the beginning, I felt the difference between KX-R pre and my precious owned Pass XP-20 immediately, but I did not feel the same way to MX-R.
But after few hundreds hours of break-in, I realize MX-R is as incredible as KX-R, they are neutral and real, very little color by themselves. Image is excellent and accurate, nothing cold or dry.
Before it fully break in, treble sounds a bit conservative, maybe that's why some people consider it is "lifeless".
Ayre R series is very transparent to the system, so any small change in your system, power quality, cables, etc., you can easily hear them. My friend always like to bring his cables to test on my system, which he can't hear the differences in most other systems. But he can hear it in 1 minute in my system.