I drived my dt990 250oohm for months with qudelix5k, and then I got fiio k7 (a proper desktop amp/dac combo) and the difference is stunning, it's not massive its just better suited for the headphones really, Idk they got mellowed and more lively with k7. As always it's subjective but i feel like more power is not necessarily better but the guts you are paying for are actually better. And yes testing them back to back with my laptop and q5k they sound harsher compared to fiio so I can actually enjoy them now.

Sound is so subjective man, one's will say it's awesome and other will shit all over your purchase, you like it that's great money well spent you don't like that return it or stop shitting on someone else's choice, some people have problem with that.

That being said, my kinera Idun 2.0 that i absolutely adore sounds the same with Apple dac as well q5k and fiio k7, no joke i can't hear a note of difference between any of them balanced or se. Some iems or headphones react differently to sources so that might be it.

Either way have fun in the hobby. Just don't spend money on stupid shit like another dongle, the one you have is great haha