I had the same experience as Ozzy did when I tried these cables. I had to increase the volume a bit as well and I felt the dynamics and extension on both ends was a little curtailed compared to my other two speaker cables.
Both of the amps I used with them and still use are the Pathos twin towers hybrid integrated amp and the Tsakiridis Aelos all tube EL34 integrated amp.
My speakers are 97 db and 8 ohm efficient.
I assume it is a synergy issue as I know the reviews are excellent. I was able to sell them for almost no loss as they are very favorably reviewed.
I guess nothing is ever going to always work in everyone's system.