I went from the V5-xe to the MX-Rs, so its not the exact same comparison you're looking for, but I listened extensively before making the jump. Also a fan of what Charles Hansen has accomplished at Ayre, I have the K-5xe and C-5xe. I think the MX-Rs really sets a new bar for Ayre, truly bringing out the best qualities solid state electronics can offer, while delivering the three-dimentionality and organic qualities that draws many to the best tube gear out there. My listening experiences over the past 6 months with the MX-Rs have solidified my original impressions, bringing an enhanced sense of enjoyment to listening. Another big benefit of the monoblocks is being able to locate them right next to the speakers (I have Vandersteen 5As) to use very short speaker cable (I use 1M pairs), a benefit which should not be underestimated. Ultimately, I am so pleased with the MX-Rs that I expect my next system "upgrade" will be the companion KX-R preamplifier which Charles seems very excited about. Charles has posted some information on the KX-R on Audio Asylum, although it would be great (now that Ayre is getting closer to releasing it) if he would give a basic overview of his design goals, preamp features, etc.
Hope this helps. - Pete -