I did get my AT-HA5050H about three weeks ago (at a "bargain" price) and use it with my Pioneer SE-Master 1 headphones (source: Macbook Pro and Audirvana; all music AIFF files).
Before I used the Pioneer U-05 dac and amp.
Big improvement in every aspect compared to the U-05.
I also replaced the stock power cable with a power cable by Schnerzinger, what improved the sound again. And I use a high end usb cable (what also makes a difference).
Did not compare it to any other headphone amp, but to me and for my taste (I'm into High End for 30 years now) it sounds as good as it gets!
Great headphones meet a great headphone dac/amp - to me a perfect match.
I know I'm listening to the music using headphones and it's all around my head and not on a stage further away. But it doesn't feel like that. There is just the music around me and this is great fun und very enjoyable. Didn't think this is possible when using headphones.
If you have the chance, give this headphone dac/amp a try!!!