Good silver often gets the "bright" rap because it is typically more transparent than copper from the midrange up, and reveals grain and other shortcomings in mediocre upstream components that copper won't reveal. It also tends to take a lot longer to break in, and can sound thin and shrill until it fully comes around.
I have run Kimber Select 1030 IC's and 3038 speaker cables for the last four years. The "Black Pearl" silver conductor in those products takes a full 1,000 hours to completely break in. They didn't sound fully right until they had logged those hours, but then everything was really right. While I was having two stereo amps converted to monoblocks, I had my old Bryston 4B-ST in my system for about a month with the 1030 and 3038 cabling. Sounded incredible. I never knew the amp was that good. My guess is that the Bryston is not your problem.
I do not have experience with Kimber's KCAG, but my guess is that it may not be fully broken in or is laying bare the truth about your Adcom preamp (which are very fine preamps at their price points -- I owned one -- but FM Acoustics, etc., they ain't). Try to put another 500 hours (three weeks of 24/7) on the KCAG with a break-in track, and if that doesn't fix it, try Cardas Golden Cross.
Good luck.
