I have been in search of a headphone that could give me the details and dynamic range of an electrostat with the tonal weight of a reference dynamic. The previous system was a K701 with a Singlepower Extreme. It gave me a pretty good sound but I felt the sound was still inferior to electrostats and bass was lacking compared to other mid fi dynamics.
 
Last year a headfier introduced us to the HE-5 at the same time as the HD800 and PS1000. While I liked the similarities to the K701, the HD800 still felt a bit thin in presentation. The PS1000 had a bit more sonic weight and I liked them as well. Then I tried the HE-5. I first heard it on the first HiFiMan amp and it sounded ok but didn't have enough juice to "crank it". So I brought them to my rig for a listen and was curiously impressed with the ortho sound.
 
Well, a fellow headfier let us borrow his LCD-2 headphones for a few weeks last fall. At that time, I was infatuated with the sound. It gave me that speed, detail and impact I was looking for. There were a few things I did notice about the LCD-2 that didn't suit my tastes. One was the laid back presentation, another was the slight recession of the highs in relation to the mids and dominating lows. I also felt the center imaging was a bit fuzzy but being a new technology (for me), I attributed this to my inexperience.
 
After reading several threads about the new HE-6, I chanced the purchase. I ordered them on the 15th and received them on the 20th of December. To have a headphone come from across the world, through US routing during their holiday season and at my door in 5 days is impressive.
 
I was happy to see the piano gloss black matched my TV, sub, etc. but the wood of the HE-5 is a piece of art (similar to the LCD-2). The cable that comes with the HE-6 is much better quality than I was expecting. Lightweight, extremely flexible, sturdy connectors & plugs, nice on the eyes.
 
I plugged them into the SP thinking no burn in time was needed and I had plenty of power because the HE-5 sounded great on it. Wrong on both counts. I couldn't get enough volume to hear vocals without distortion. Any extension from the mids on either end was unbearable. Having heard the burn in of the K701, I knew not to react to initial impressions, so they were left on for a couple days. Coming back to them was a much more pleasurable experience. I could hear beautiful sound. Something didn't sound right but I was having a hard time identifying what it was. For one, I couldn't get enough power for preferred listening. Every time something got me excited, my amp ran out of steam and would distort in the lows. Something I'd not experienced with K340, K701, HD800, RS-1, etc.
 
The other thing I had a problem with was the center presentation. Both side sounds were clear, in place and localized. When panning, everything tracked through from ear to ear. But playing music sometimes, the center presentation seemed to be out of phase, soft, fuzzy. I noticed this with the LCD-2 so I thought it was perhaps the technology.
 
Well I kept reading about trying a speaker amp to run them and I had one I could control the volume on the amp (Rotel RMB-1050). After I got the volume pots trimmed for my listening levels, I couldn't wipe the grin off my face. Not only did I hear what I wanted, I heard what I didn't think could be done with a headphone. Deeper bass with better details than any headphone I've heard up to that point and most speakers/subs. The highs were comparable to stats with just a bit less decay and not quite as delicate. Much better than I've heard from any dynamic. The best part was that the center resolution issue disappeared. Seems I just needed more power.
 
I am a tube convert and wanted to try a tube speaker amp but the only way to control the volume is by the computer (right now). So a fellow headfier offered me an amp to try (GTA SE-40). I have to say, a tube speaker amp with good extension and little roll off is a treat worth the investment and time. I have found my sound and am indeed a very happy camper. Now to get a DAC (Perfectwave maybe) worthy of the setup with a volume control and I can listen to music and not equipment until my ride comes to take me home.
 
If you like the Sennheiser sound, the LCD-2 are your babies. If you like the AKG sound, the HE-6 will be the ones. For the price of the HE-6 and a nice quality tube speaker amp, you can get a pretty good rig for under the cost of a HD800.

When I first got the K701, I had been using the Ety 4s so the bass was actually better on the 701s. They did sound tinny and shallow. I read that they needed about 400 hours of play to settle into the final character they will provide so I left them on along with a new tube amp for three weeks non stop. If they were going to fail, I wanted them to do it early in the warranty.
 
They did indeed respond both to moderate volume material and a more powerful amp. As I became more knowledgeable of the nuances of the sound, I started tweaking the cables, tubes and power cords.
 
I can say that while other headphones in the $250 range may have looks or a "wow"sound initially, I have always come back to the 701 for most of my listening. At this price range, I don't think you can find a better potential headphone to build a system around.
 
The audio quality of the headphone is based on balance. No one area of the sound is dominant. Some prefer a strong bass presentation and others prefer more highs be dominant. This headphone will earsmack you if the material presents it and your amp can deliver it. Otherwise the sound is distilled and smoothed. For acoustic and vocals, they do an admirable job. I enjoy early era progressive rock and acoustic rock with them. Anything more energetic and I have to change to the RS-1.
 
I am not a bass head but the 701s are bass lite. While the note is presented down to 35-40~, there is little weight unless the material highlights it. So listening to a bass groove will not stand out with the other music unless they are solo. But when listening solo, you can hear the pluck of the string by the finger, the leading edge of the note is solid and decay believable. The highs are a bit prominent. If your ears are young and treble sensitive, these could get fatiguing.
 
In deciding the value of these, keep in mind that you will need quality source material and amp to hear them at their best. Poor gear/material will be exposed. A solid state or hybrid amp is best suited for these because of their balanced presentation. I like tubes better but will cost more to get the same performance. AKG recommends 200 mv max. I'd recommend an amp with at least 500mw.