I had read an awful lot of material about TUC before sending my EMM pair to David Schulte and did not find much negative feedback from those who used his service. I reluctantly sent this very expensive digital front end in about two years ago, and I was surprised how, after about 200 hrs. breakin, the improvement over stock. I am lucky enough to have had a stock EMM pair on hand for comparison. Whatever he is doing seems to raise the performance level of even the highest high end gear.
Recently, I sent my Bel Canto PRE2 to David, and I am now breaking it in. Right out of the box, there was a noticeable increase in sound stage and clarity, so much so that I had to decrease my default volumes by 2 dB. The sound was not louder, only bigger and more three dimensional. There is really not much risk, since he provides a 5 year warranty and a buy-back clause if you are not pleased with the work. On other forums (like Audiocircle an Audiokarma) there has been a lot of negativity, mostly from people who have not had the opportunity to judge the work of TUC. The big sticking point is the lack of detailed information about what is actually modded inside. Unlike Modwright, David keeps details secret; and, that is what raises the suspicions of doubters about whether he is doing anything major. My experience, along with the ability to A-B stock vs. mod, has been nothing but positive.