Since the topic is on 555 ps DR, i just share one of my experience. I first bought one to pair w my nDAC. Didnt hear much uplift from it which my dealer also surprise to hear my comments.
At one point was tempted sell it away, however along the way i upgraded to a full 500 series which the nd555 came in last that made me kept the 555ps dr. Overall, now im enjoying the 500 series.
Till date, perhaps alot of members would shoot down my comments on how could a 555 psdr not make a great jump on a nDAC… 