Honestly, the problem is pretty unique to the HE6se v2 and a small handful of other headphones still on the market. The HE6's problem in particular is that it is a bit of a dinosaur, based on driver design that is almost 15 years old now. These days, most modern headphones will sound just fine on most modern amps and you don't have to worry about any of this. But the dinosaur HE6, unfortunately, really does benefit from every watt you can give it.

What the HE6se V2 can sound like when properly amped is very raw, energetic, aggressive, ultra-detailed, ultra-fast, great bass slam, etc etc. Properly amped, this headphone can keep up with others three or four times its price. Without adequate power, the bass slam and speed vanishes, the soundstage narrows, and the highs lose all energy and become very vague and dull. Sounds like a completely different and just much worse headphone.

For instance, the way I normally listen to my HE6se V2 is by connecting it to the speaker taps on my Onkyo AVR that's good for 150WPC@8ohms (which is about 24WPC@50ohms). I'll be the first to tell you that this is extreme overkill, that much power is absolutely not necessary, but 1) it certainly eliminates any doubts you could have about providing adequate power, and 2) the AVR only cost me $100 used. Driving the HE6 this way, the wattage-to-dollar ratio is out of this world.

So my overkill Onkyo AVR is my point of reference. It allows me to hear everything that people endlessly praise this headphone for. And so from there, I experimented with how it sounds on other amps I own. The least powerful amp I tried was my little Liquid Spark, which is good for about 1W or so. Totally inadequate. No slam, no speed, no energy, etc. Honestly just bad. I love the amp for a lot of headphones in my collection, but it just doesn't cut it for the HE6.

It wasn't until I bumped up to my Liquid Platinum, which is good for about 4W, where I really started hearing that greatness that I was hearing with my overkill Onkyo. Such that if all I had was my Liquid Platinum, yeah, that'd be fine. I would say the LP's 4W is enough to get you nearly everything this headphone can deliver. It turns out that I don't really care for the planars-on-tubes sound, so I don't pair them often, but I found the LP to be technically capable for sure.

The community for this headphone on Head-Fi, we find that amps like the Liquid Platinum or the Schiit Jotunheim are about as low as you want to go in terms of wattage to extract most of what this headphone is capable of. One lesser-known amp that's been getting a bit of attention lately from HE6 owners is the Emotiva BasX A2m, which when set up in direct drive mode, is good for a whopping 8.5WPC@50ohms, and the amp only costs $350. Good bang for the buck.

All of the amazing things you hear people say about this headphone, honestly it's 100% true, it's real, the headphone can do it. Unfortunately, unlike modern headphones, you do just need to work for it. That's not to say you have to spend money to get there. Like I said, my Onkyo AVR I use with mine only cost me $100 used, and there is a good crop of dedicated headphone amps available new today that have adequate power without absurd price tags, like the ones I mentioned earlier. Just... some specialized gear is unfortunately required to really extract every ounce of greatness out of this dinosaur headphone.