Getting into the world of audiophile and got a question

So where I am at right now is I have FiiO brt3k on its way (amp/dac) and I own dt990 pro. This is, the dt990 are too sharp for me- WAY too sharp. So I am looking at other headphones.. On this here Drop site there be the HD6xx, I can afford them and the sound profile is not even sharp, so I know that will be ok. Just the only issue is now my Amp wont be enough? or perhaps it will. The amp is rated for up to 100 ohm. The thing is, my current 250 ohm headphones work in my normal smartphone and get loud enough, just perhaps not best sounding... so with the HD6xx being only 50 ohm more, it would not surprise me if the brt3k can power them just fine. that all said and done im pretty sure its to do with the headphones sensitivity and not their impedance when it comes to what can drive what- but i do not know how to check for my dt990 sensitivity vs the HD6xx's any help is appreciated :)

Jan 5, 2021
So I own a btr5 and previously a 6xx. In terms of will it drive the headphone and produce sound, yes absolutely. One thing worth noting however at least with the btr5 (and id assume the 3k) the balanced output vastly outperform a the single ended in both power and quality however that would add some cost to the 6xx for the correct cable. I don't personally prefer the sound of the btr5 driving full sized headphones from the single ended and would say you'd be better off with a budget desktop amp like a heresy or atom