This is an old thread but I received great help from many members and I would like to document my findings over the last month.
A. I kept contradicting myself when explaining symptoms (which was not helping members to recommend solutions). What seems to work one day was not the day after and vice-versa. The reason for that is that nothing was stable and the problem evolving depending on when I was listening. I have not identified 100% of the pattern but it looks like the following: No issue until 6 pm (week days) followed by serious degradation until 10 pm, then fine again. The pattern is a bit different during week-ends. First conclusion: most likely power grid pollution, may be internal to my house or external (my street, etc,).
B. I was able to narrow down suspects: NUC (and laptops as a substitute to the NUC) - both using switching power supply. I received a Low Noise LPS (ebay, China type but still decent) for the NUC. That was a miracle (keep in mind I am an Electrical Engineer and I am skeptical of many things that sounds to me like snake oil). YMMV but for me LPS was the solution (almost, keep reading) to my problem. What was good before became excellent and what was terrible (at specific hours) became very good sometimes and good at other times (I suspect some degradation remained during the worst moments of the evening but I cannot confirm). I was in love again with my system and started to lesson every night for 3 - 4 hours straight with my spouse.
C. But I wanted more, better... I sold the Audio Alchemy DAC (which is very good by the way, very detailed) and now I have a Lumin D2. I do not really believe in electronic burn-in (I do believe in warm up, which is very different - a subject for another discussion). OK, wrong again (may be, or not… could be related to the time of the day). My wife made me notice how better the Lumin was after a few days. Missing the details the first day the Audio Alchemy was so good with, the Lumin started to be more and more detailed (not as much as the AA), and especially started to expend the image and the overall coherence between the different instruments. But I noticed that part of the degradation was back with the Lumin (which is using an internal switching power supply). For example, last time around 6:30 pm, we started earing the degradation during a specific song. Started good and degraded down to terrible. Played again the same song since the beginning and was terrible. Second conclusion: my system does not seem to like switching power supply, at some time of the day.
D. I ordered an other Ultra Low Noise LPS for the Lumin. Waiting for it (as a note, I know it will most likely void my warranty - so be it). I have great expectation it will solve the issue. BTW, the Lumin is fantastic. If the LPS does not work, I will have a D2 for sale... But I want to keep it so bad (until I upgrade to a T2!).
E. What is next? I need to improve electricity quality feeding the system. Not sure what will be my next move since I do not know the cause of the problem. My intents, in that order: 1). Elimination of all Switching power supplies near or on the same power line as my system; 2) Adding a LPS to both my modem and switch to replace their switching PS (not convinced of the result but it will cost me around $200, so I will try); 3). Add additional filtration to the system, may be something like an isolation transfo that provides balanced power and filtration. I already have some filtration in place but quality could be way better; 4) In my dream, because the amount of work will likely prevent me of doing so, adding a dedicated power line directly from the electric panel - this is what I have done for my cottage and my HT in the basement and I see value; 5) what else, don’t know - may be someone would have a suggestion?
