Mad Scientist IC’s

So in another thread, I described having issues with audible speaker hum when I connected my Jolida dac directly to my NuForce STA-200 amp via a pair of Schroeder-Dueland IC’s.  Lots of discussion regarding the high gain of the NuForce and the output impedance of the dac.  A few weeks ago, I purchased a pair of Mad Scientist HAC+ IC’s from MrTriode (who btw is a great guy to deal with), which after proper break-in, replaced the Schroeder-Dueland IC’s. First off, they sound amazingly detailed and three dimensional in my system.  Second, the hum disappeared altogether.  Going back to the Schroeder IC’s reproduced the hum.  So I’m curious— the Mad Scientist’s use carbon fiber; the Dueland’s, tinned copper.  What difference in the materials used eliminated the hum?