The HE-6 is an absolute power hungry beast of a headphone that people connect up to speaker amps (so Ive just been told recently :bigsmile_face: ) so you may really want to consider whether the HE-6 is going to be run at anywhere near full potential off a portable amp.
These are excerpts from the Headfonia review of the mk3:
"The balanced configuration in the Mk3-B yields very powerful results, and the Mk3-B not only drives both the Hifiman HE-500 and HE-6 better than RSA’s SR-71B and Ibasso’s PB-2 portable amps (both balanced models), or Triad Audio’s gigantic L3 amplifier, but also better than a lot of mid-fi desktop amplifiers, and better than most high-end tube desktop amplifiers. It still doesn’t kick like a good speaker amp with the HE-6, but it’s really a good combination and one of the best amps that I’ve heard the HE-6 with.
I admit that I’m a big proponent of bigger is better, and so I’ve always been a big fan of humongous sized desktop amplifiers. How the Mk3-B is able to drive the HE-6 with very good results, frankly speaking, still puzzles me. I’ve always told people that the HE-6 is best used with true speaker amps, because the reality is that the HE-6 is the hardest headphone to drive today, exceeding even the speaker-like AKG K1000. So I talked to the guys at ALO about how they were able to do this. They mentioned the use of the same op-amps as on the Mk2 and Mk1, but in bigger quantities. Other than that, the input and output sections are different than on the Mk2 and Mk1."
"The real magic happens with the Hifiman HE-6. Not only does I have no problem getting enough loudness on the medium gain level, but the amp also has a really good synergy with the HE-6. I’ve always been a bigger fan of the HE-500, but that’s probably due to the fact that most amps I review can’t drive the HE-6 right. The HE-500 is much easier to drive than the HE-6, but in this case, I can see why the HE-6 remains the flagship model, it’s just far more impressive on the Mk3-B."