Not a review, just another data point. Received my Fa-10 2 days ago, so the amplifier is not burn-in yet. Having said that, I think I already found which headphone I like with the amplifier.
My current reference set-up is Rockna Wavedream dac- DNA Stratus- Hifiman HE-1000SE. Yes, I prefer HE-1000SE with Stratus over HD800 and Focal Utopia. The reason why I bought FA-10 was because I wanted a solid-state amplifier sound where the image is sharper, bass is more defined and background is blacker, to compliment my tube amplifier.
I tried the Fa-10 with HE-1000SE, ZMF Auteur, Zenith PMx2, HD-650 and Meze Rai Panta iem. I had wanted to use Fa-10 primarily with HE-1000SE, but I was disappointed that the combination didn't turn out to be what I like. While there is sharper image and more details, the tonality just did not sound as organic. HE-1000SE on my Stratus sounds more realistic.
Next I tried ZMF Auteur. It is a headphone that I hardly use because it just can't match up with HE-1000SE, whether with Stratus or with Cayin iHA-6 which I previously owned. However, on Fa-10, the headphone was elevated to my new end game combination. I never expected that Auteur can sound so good! With Fa-10, the combination provided everything I wish for: big soundstage, highly musical, realistic and non-fatiguing. To think I almost thought of selling the Auteur away a few months ago.
No doubt Fa-10 is a very capable amplifier, but I think alot still boil down to synergy and your other equipment. I am glad that I found a very high performing combination with the Fa-10. Thus it is a keeper in my book