Regarding USB issues; synergy, synching, filtering, power ect. I would actually place good money on that few, if any, could hear the difference in a blind test between streamed FLAC via USB and a SACD.
There is however a big difference between a crappy dac and a good dac, and also a big difference between mp3:s and FLAC. When we go into details like cables and stuff, I think many decides to hear a difference than actually doing it. Many times I think a good ear wash is a better investment.
Came to think about this guy: https://www.youtube.com/watch?v=rjTQsY8rhaM
You could quite easily flip those examples round and people would agree; little difference between 320 MP3 and lossless, big difference between USB / SACD. Horses for courses; perpetual objective discussions based on subjective experience.
When myself and a friend played music through the MSB stack and swapped from Quad USB (SOTM SMS100) to I2S (UMT) the difference hit you in the face. Even my wife would pass that blind A/B very easily, and she's happy with in car speakers. if you choose to believe I'm making that up, so be it.