Does this say it is difficult/impossible to build a proper discrete DAC? No, it is more like making sure all of your 20 bit DACs in production are just that; in Singapore, Alaska in winter, or Key West. There could be nothing worse than making production quantity 20 bit DACs until you realize some are 12,15, or 21. It is more like building a highly tolerance precise, labor intensive, parts matching, temperature controlled DAC which would be difficult to exactly duplicate, sample to sample. Am I ever going to build it? Who knows? I have thought about it since the 1980s. If I were to do so, I would not use either one’s (sign magnitude) or two’s compliment. I would use an old coding designed to be used on polar co-ordinates which I feel would be the absolute best to decode music. I would put it in a temperature controlled oven and agonize over how to solve the switch variation problem. It is a bucket list item for me. I know I could make two the same. But two thousand? Probably not. Maybe I could learn.