I'm a lucky guy, I've heard most of the world's very best headphones: Sennheiser's HD 800 and their legendary Orpheus, the Audeze LCD 2 and 3, the Stax SR-007 ($2,600), SR-009 ($5,200), and now I'm spending quality time with Hifiman's flagship HE-6 planar magnetic headphones. I've long admired Hifiman's designs, starting with their very first model, the HE-5 back in 2009. The HE-6 looks nearly identical to Hifiman's current HE-4, HE-400, HE-5LE, and HE-500 headphones, but the HE-6 is heavier (502 grams), and it feels like it's built to last forever. Comfort levels are good, but the HE-6 can't match the Sennheiser HD-700 for long-term comfort.
The HE-6 ($1,299) is a beast to drive, and most headphone amplifiers, including some of my favorites like the Burson HA-160 don't have enough juice to really energize the HE-6 to its full potential. The new Burson Soloist get close, but still not completely there. Few amps were powerful enough, so Hifiman bit the bullet and crafted an amp to fully exploit the HE-6's capabilities. It's called the EF-6 ($1,599); it has two headphone output jacks, a standard 6.3mm one, and a four-pin XLR headphone jack (for use with the HE-6). The EF-6 also has two stereo inputs and separate stereo outputs that can be hooked up to another amplifier to drive speakers. EF-6 delivers up to 5 watts per channel to the HE-6; most high-end headphones are perfectly happy with one-tenth the power. I used the EF-6 with all sorts of full-size headphones, and it always brought out the best in each one.
The Hifiman headphones and amplifier provide a remarkably direct connection to the music, without adding or subtracting much from the sound. It's as close to "being there" as I've heard from headphones.
The Stax SR-007 and -009 are more transparent and clear, but to my ears those two headphones miss too much of the music's body and soul. The sound is vivid as can be, but dimensionality and visceral kicks of live music are missing from the Staxes. Aerosmith, or any hard rock doesn't connect over the Staxes, but the HE-6 is a total party animal. Play a pure audiophile recording and the HE-6 will bring the music to life. That's why I prefer the HE-6; there's no edge or harshness to the sound. Live music is effortless, it's just there, and that's what the HE-6 does so well.
The Audeze LCD 2 is in the HE-6's ballpark, and it's even more dynamic and visceral, but the HE-6 is more natural and transparent. They're both superlative, and it would be hard to pick an outright winner, assuming you were using a headphone amp that could drive the HE-6. The EF-6 can with ease, but most amps cannot; the LCD-2 is less demanding, and works with most high-end headphone amps. That said, the LCD-2/EF-6 pairing was truly exceptional.