I just want to share a listening experience I had with the he-6 recently. But first I'll give a brief history of my personally journey with them. I've long been a proponent of the he-6 sounding best with speaker amps. In fact, I came to that conclusion before they landed to my house based on my experience with previous hifiman orthos I've owned. And given these were going to be more inefficient than even the he-5, I already had planned on paring them with speaker amps. So now that I've got that out of the way, a friend of mine(headfi user The Wuss) got them around the same time I did. And both of our journeys were very different. Some of the amps he used were little dot mkvi, spl phonitor and such. At the time he thought the mkvi could drive them and thought they sounded really good. He also liked them with the phoniter, and loved the soundstage they had off the phonitor, but always thought something was missing. And as a result, he had them ranked behind his lcd2, and T1.
I had went through about 10-15 amps with many of them being vintage, and each one had the strengths and weakness, but I was already under the impression that these headphones were pretty special. So one night we had a two person meet, and he listened to them off a pioneer sx1010 I had at the time. I told him out of all of my amps, I would have ranked the sx1010 last, but it still did a great job driving them. His jaw literally hit the floor. It was like hearing them for the first time. So this eventually led to him getting the dark star. And when we met again, we both determined the dark star was the best we ever hear the he-6. But with how drastic the changes were going from one amp to another we also surmised that we probably still haven't heard the best of the he-6.
The dark star was the first(and to this point the only) dedicated headphone amp that I had listened to that could match and even beat a "good" speaker amp with the he-6, and although I've come to own a couple of speaker amps I like better than the dark star, that combo is just simply magical and amazing. He also owns the lcd-3, and I hold them in very high regard. They are the second best headphone I ever listened to next to the he-6. But on the darkstar, they still are on the same playing field with the lcd-3s doing a couple of things better, and the he-6 doing quiet a few things better. But the dark star is good enough for me to prefer them both to the r10 which is still the best pair of dynamic cans I ever listened to.
Now all of this brings me to our most recent meet. Brent recently purchased an audio research vsi60 with the sole purpose of using it as a speaker amp for his new harbeth hl5. He has no intentions of it being an he6 amp. He really adores the dark star, and that amp is end game for him(I can't really argue with him). But given my recent experience with a couple of amps I have, I told him he should at least try it, and that I believe that amp on the he-6 would be on another level than even his dark star.
The he-6 he has been hard wired and terminated with two 3pin xlrs, so they were a no go with his 4 pin xlr to banana plug adapter, so I had to bring mine. What we heard that night was nothing less than stunning(well not for me). On the dark star, I slightly preferred the he-6 to the lcd-3, but on the AR, it wasn't even close for me. The mids were the most realistic I've heard from any transducer, and that includes a pair of 40,000.00 jm lab utopias(those were the previous best for me). There was no treble tilt was so ever, and the bass had unlimited extension. The bass was even better than the lcd-3 for me. images were coming at me from all over the room. It was simply the best sound I ever heard in my life, and with all of the 20,000.00+ speakers I've listened to and headphones I've both owned and listened to, that's really saying something.
So by the end of the night, we both said that same thing we have said previously. And that was, I bet we still haven't heard the best of the he-6. We both began to throw out hypotheticals like, 20,000.00 tube monoblocks, and 20,000.00 sources etc. Or even 10,000.00 monoblocks and sources. This is a headphone, that I believe that has virtually unlimited potential unlike any headphone I've ever encountered. Sorry for the long soliloquy, but I just wanted to share.