My experience completely mirrors Stringreen's. I auditioned the MX-Rs in my home on W/P8s with both Cardas GR or Transparent Ref XL or Ref MM cabling and came away thinking the MX-Rs were somewhat arid and not for my system at the time.
I later heard the MX-Rs powering some Vandersteen Quattros through Audioquest Sky cabling with astonishing results, causing me to rethink my initially tepid impression of both the MX-Rs and the Vandys.
Simply proving Audiofeil's point once again, but also seconding Stingreen's recommendation that you try Ayre equipment with cables beyond Cardas/Ayre with Audioquest and Anti-Cable topping the trial list.