Are you sure you are actually hearing that? You can't be sure if you haven't done the comparison blind.
If you are hearing a differece, it is most likely coming from the filter at 44.1kHz rolling off slightly in the audible band. However this is at such a high frequency and at a pretty low level (If you have a (correct) sharp filter selected) then you are pretty unlikely to be able to hear that unless you are a teenager.
Possibly you are more likely to hear it if you have selected a slow roll off filter in your DAC - if it has selectable filters.
I have tried with various DACs, actually hearing with the headphone output of my Focusrite Scarlett 2i2 4th gen. and Sennheiser hd 600 and i notice the same difference.
As you said is more audible in the highs, is subtle but as I mentioned above I have a huge congenital visual impairment and I trust a lot on my hearing.
Perhaps this explains why I’m able to perceive those differences: I don’t think I can hear above 15.000 Hz because of my age (this relays on physical aging process on the inner ear and not on the acoustic cortex of the brain) but I’m quite sensitive to minimum color changes of the sound.
Love the combination of Scarlett and Sennheiser, by the way: my Ifi Zen Signature colors a lot more and costed double the price, actually I sell it on Wallapop
P.S: I’m not saying that 44.1 kHz settings sound bad, just my representation of the sound scene is not as satisfying as the one I listen on the max. quality setting. I have a neuronal phenomenon called synesthesia: for me frequencies are identified with visual positions, lows are perceived as near the ground and highs goes more to the celling. In stereo imaging (despite I’m actually listening with headphones with one single driver) I can see a rectangle if the representation is complete and flat. Sometimes, depending on the system used I see an elipse stretched to the sides, without the high and low corners of my reference rectangle. For example with humble apple earbuds (cabled, bluetooth I cannot support it).
When coloration happens, as with my Zen Dac, I can see the rectangle stretched in some sides (midhighs and low bass), the vertical sides corresponding to the frequency response curve I guess…
People usually have horizontal representation of the stereo image, wider or narrower, center focused etc. Mine is bidimensional as a cinema screen and frequencies play the role of vertical axis.