Just about to pull the trigger on Pontus 15th ...

@sls883 @larsman  The issue is gone—I really had no clue what happened. I switched to other outputs/inputs (coax, TOSLINK), and it worked fine. Then, when I cycled back to I²S, the issue disappeared.

Overall, the image seems focused a bit over Smsl ddc.  The very affordable smsl seems able to reach 85-90% of the U18.  Not bad at all as several reviewers / users pointed out.  The U18 has much substantial weight due to the toroidal transformer though for its low-noise power supply.  A compelling price proposition at $399.

Does the title of the thread indicate that the OP wants to shoot up a DAC?

There's a few that deserve it.

@lanx0003 Good deal.  Glad it's working for you. 

@sls883 @mattw73 

I guess I was mistaken about the µDAC. I kept playing it—with only a few short breaks over the past days—and have now accumulated another 50–60 hours of music playback. At this point, it probably has around 110–120 hours of music playing time and about 140 hours powered on. The layering has finally come through, and the congestion in the low-midrange and upper bass is gone.

Coupled with a wider soundstage (compared to the D90), my listening experience now surpasses what I had with the D90 and has never been this satisfying. The D90 still delineates notes more precisely, but the more homogeneous sound field produced by the µDAC makes the overall presentation feel more natural. And that rich, slightly more forward midrange is simply second to none.

Thanks to both of you for walking me through this. That said, I hate to admit it—this means I now have to keep another DAC… while the third one (Gustard X26 III) is still on its way.