Fidelio X2, DT770 (250 Ohm) or NAD HP50?

Hi,

I've been thinking about getting a new pair of headphones for home usage for a while now and I wanted to get some advise from you guys and u/ZeosPantera. I currently own two different pairs of headphones, the Audio Technica ATH-M50X and the Sennheiser HD558 (Stock).

My source is a NAD D1050 DAC with a built in amplifier capable of powering up to 600 Ohm headphones.

NAD themselves does not have the Output Impedance listed on their site nor will they tell you if you contact them. But Sound&Vision rated it as 15 Ohms, which if true, is a bit much as far as I know. Full specs can be found here.

If 15 Ohms is a bit much for low impedance headphones such as mine and similar ones I might buy in the future, a standalone AMP recommendation will also be appreciated.

I will listen (and watch) to all kinds of content on this new pair of headphones, such as highly compressed Twitch streams (160kbps), Spotify, FLAC/ALAC, Netflix and gaming on a PS4 (connected to my DAC) etc.

And now on to the headphone part of this post.

I've been looking for a new pair for several months now and I have come to the conclusion that I might need something in between my M50X and my HD558 in terms of sound signature. I’m not sure whether I should go for a closed or open pair. If it’s an open back headphone it really depends if there’s enough bass and how much sound they leak outwards. Since I generally have my headphones on pretty loud volumes the inwards sound leak will probably not be an issue.

My Sennheiser's are very comfortable and sound great for general use and games. But to me, they're a bit boring when it comes to music and movies.

My M50X's are alright with music/games and great with action movies. But they’re a bit too boomy (at times) and the highs are very harsh (to my ears). Sometimes I just have to lower the volume because there’s simply too much treble.

I think something like my HD558’s in terms of highs but with a bit more bass and mids is a good place to start.

If I were to EQ a fairly neutral pair of headphones, I would probably increase the bass a bit and decrease the treble slightly (in the upper range at least).

The headphones I’m eying right now is the Fidelio X2, NAD HP50, Beyerdynamic DT770 Pro (250 Ohm) AKG K7XX and B&W P7.

Thoughts?

Cheers

EDIT: I though I should mention that I find that my Sennheiser HD558's to leak a bit too much on high volumes, if any of the open pairs I'm mentioned leak more than mine, I may or may not have to look elsewhere.

EDIT 2: I realized that I haven't mentioned that I'm located in Europe. Which might influence the final decision with the extra cost of importing goods from the US that are not sold locally.

EDIT 3: Does Massdrop avoid VATs and import fees with their freight forwarding option?