J.C. Verdier 845 monos- anyone heard them??

I own a pair and love them. I upgraded the tubes, the best improvement came from switching to 845M tubes from "supertnt" web site. My wife says she hears a high pithed ringing noise when I use these amps, but I can't hear it. According to Ming Su, the distributor, he only imported four pair to the U.S. goto www.rowlandhifi.com to get my contact info if you like.

I owned these for about 9 months and thought they were one of the best 845's I have heard or owned. I would put them up there with the Komura's and Nagra's. They are very well built and very nice looking amps as well.
I also experienced an inmprovement with the 845m's

I just got those amps.
I love them.
What kind of improvement did you notice with the 845 M tubes ?
Did you have to adjust the bias ? Mr Verdier told me that we would have to if we change tubes...
Thanks in advance !