Some changes are hard to hear. I had that experience with speaker cables, years ago. While many components need to have been powered up for awhile to sound there best, I’m personally skeptical of a break-in phenomenon with a piece of electronics. Having recently changed speakers, my experience may be of some value. The new speakers KEF LS-50s, have a slightly more extended top end than the Joseph Audio RM-7si Signatures they replaced. But the difference goes beyond that. I’ve decided that one of the qualities one pays for in better equipment is that the good stuff faithfully reproduces the really small stuff that lesser equipment simply swallows up, kind of the way a “noise gate” operates in a recording setup. Some people call this “resolution,” others call it “micro dynamics” (which actually is a different quality that depends, in part, on the transmission of those really smal signals. Anyway, the LS-50s seem to do better at the little stuff than their predecessors.
so, the question is whether the rest of the elements in your reproduction chain are good enough at reproducing the little stuff to show the difference made by your new DAC (assuming there is one).
Regarding ptss’s suggestion of balanced power: don’t be so quick to dismiss it. I bought an Equitec 1.5kva balanced power system some time ago. It made an immediate and dramatic difference in the SQ of the Stereophile Class B CD player that I was using at the time. Much to my surprise it made an equally large difference in the quality of my now old, but “Class A” Sony SACD player, which was a far more expensive unit. Run straight out of the wall, the sound was somewhat two dimensional and suffered a problem typical of digital, “dirty” high frequency transients evident in the reproduction of such things as crash cymbals. There are technical explanations for this, which I won’t go into. I would think, at some price point, a digital product would not benefit from balanced power, but I don’t know where that point is. I’m generally skeptical of power tweaks, especially devices that feature all sorts of clever scientific-sounding names for their “features,” but balanced power is the real deal. The “derived ground” that balanced power provides seems especially important to digital systems, and the magnetic energy stored in the massive BPS transformer (80 lbs.) seems to be particularly helpful to the power supplies of subwoofers, that don’t use big, expensive electrolytics in their power supplies, giving them better transient performance and subjectively greater extension.
Final question: do you have a friend with a good system that you could use to do your comparison?