I have had a Lumin U-1 mini, D2, A1, and X1. I can tell you each of these DAC's was a definite step up, especially the X1. The D2 was so average sounding compared to the X-1. The level of detail for each DAC was easily heard.
I then decided to go to an all-tube system and now have a Lampizator Pacific. To be honest there was not a major step on in SQ between the Pacific and the X-1. However, once I added a Lucas Audio Music Server, the SQ jumped 3-fold. The advantage of the Pacific is that you can tube roll to change the sound. That is a major benefit. I have already ordered the Lampi Horizon and I have done A/B comparisons of the Pacific and Horizon. Again, the level of detail is just accentuated.
So IMO there is a major difference in the sound of DAC's as you go up the ladder.