@markusthenaimnut -- I wish I could give you a more detailed comparison, but I have only had the Sachs preamp for a couple of weeks and am still waiting on Don's KT88 amp--which I also ordered-- to arrive. In the meantime, I've been using a pretty old, pretty cheap solid state amp with it, and the sound is surprisingly good. Even with these limitations, my first impressions of the Sachs preamp are positive. I can only imagine how good my system will sound once the amp arrives.
It has been about ten years since I had the Supratek, one of the few pieces of audio gear I regret selling. I am confident that Mick's latest iterations of his design are even better.
I think it is highly likely that they sound more alike than different--very liquid, layered, dynamic, and musical. I have always been partial to preamps that employ the 6SN7 tube.
I doubt this is very helpful, but it's all I got for now.