Pros: Exquisite detail and separation across the entire spectrum, resulting in a neutral yet very natural sound. Comfortable, and modular.
Cons: Requires more power than most mobiles or on-board sound cards can provide. Open, so you can't use them in public.
I have used these directly connected to my Creative X-FI Fatality Pro sound card, then through my Fiio E11 and Bravo Audio V2 amplifiers (separately). I have also tried them with my Sansa Clip+ (Rockboxed) and my Galaxy Nexus phone, both paired with the Fiio E11. I have owned them for a little over 2 months now, with over 100 hours of run-time on them.
I tested these with various media formats (OGG, MP3, FLACC) at various bit rates (128kbps – 320kbps). My operating system is Xubuntu 13.04, and I am using the default ALSA driver. I use Audacious as my media player with EQ off. I enjoy all genres of music from many different era's, so I prefer a neutral sound signature with adequate but not overpowering bass. Below are some of the other headphones I currently own.
Sennheiser HD 558, HD 25-1 II, CX-200 Street II
AKG K142, K403, K350
Sony MDR-V700, MDR-V300, XB700, XB500
Am I a true Audiophile? I am proud to say yes, yes I am. I am not really sure why people are hesitant to call themselves an audiophile. Maybe they think it's some elite cult you have to be voted into or something. In any event, the definition of audiophile is "a person who has a great interest in high-fidelity sound reproduction." I would venture to say most people who invest in these headphones fall into that category, whether they know it or not.
However, because I have a wife and two kids to feed, I can't afford the $$ or time to get the setup some people have. Yes, that means I can't afford a $300 cable, or a $3,000 amp. That means I am your average Joe audiophile who has to think long and hard, to squeeze the best sound out of every dollar spent. Because of this, I think my setup is likely very close to what most people might have who are considering a headphone like the HD 600. And let me tell you now, you do not need a $1,000 budget to get high-fidelity sound.
From the satisfying "click" you get adjusting the headband, to the sexy looking speakers behind the steel mesh, you get a sense of quality and style that justifies the price. The padding (velour) is soft and plush, the clamping force is just right. The paint job is akin to a granite counter top. When visually comparing these to the HD 558, you can tell it's in another class entirely. In addition, Sennheiser has managed to make them even more comfortable. I wear glasses, and I have worn these for 6+hrs straight with no discomfort whatsoever. This is quite a feat considering the heavier and larger construction.
The replaceable cable is slightly thinner and allot lighter than the 558. The isolating material on it is soft and slick to the touch, vs the rubbery, sticky feeling of the 558 cable. It is terminated to a standard straight 3.5mm, but includes a really nice 6.5mm adaptor. When the adaptor is on, you would think it's actually terminated to 6.5mm. I was actually fooled into looking for a 6.5mm to 3.5mm adaptor in the box. I had issues connecting my 558 to some mobiles with the bulky adaptor, not an issue with the 600.
This is a completely open headphone. In comparison to my other open headphones, it seems to "leak" sound out the most. I am not sure if it's because they have larger drivers, but people in the room will definitely hear your music, even at low levels. At times the wife watching TV in the same room (15 ft away) will ask me to turn them down, albeit only when I crank them. But this design is part of the reason it sounds so wonderful. Just be aware this is not something you want to be using in public.
In terms of durability, this has stood the test of time, and even if you were to have an accident, nearly every single part can be removed and replaced on this headphone, including the speakers themselves. In this regard, it is just like the legendary HD 25-1 II. Best of all, Sennheiser does not charge you a premium for replacement parts. This gives you piece of mind and a sense of belonging. Once your in, your taken care of for life.
I have heard many headphones, but none gave me the feeling this one does. The closest would be the Grado SR60i, the one that got me started in all of this to begin with. I purchased many headphones since, but none sounded significantly better, until the HD 600. If I had to sum it up in one word, it would be "mouthwatering". The detail is so raw and natural, and the separation of each note across the entire spectrum (even bass) is exquisite. Particularly impressive to me was the depth/texture you hear from instruments (and vocals), from drums to violin, and everything in between. Everything the SR60i does well, the HD 600 does better, and everything it lacks (bass/comfort/design), the 600 does masterfully.
The experience is best on acoustic or live recordings. More complex compositions like you find in classical or rock, or anything with great vocals, are fantastic too. Honestly, nothing sounds "bad" with this headphone, those are just the area's where you can easily tell the difference when comparing it. Those who primarily listen to electronic, with allot of bass, might not appreciate everything the HD 600 is capable of.
Do you need an Amp?
Probably the most commonly asked question about this headphone, so I give it a section of it's own. The short answer is, try it out with what you have first. You will be surprised at how easy these are to drive, despite the high impedance. When connected direct to my X-FI Fatality Pro, volume was sufficient for me at 45%, on quieter tracks I would go to 60%. As reference, the HD 558 and SR60i would require no more than 30% on the quietest tracks. I could still experience the headphone in all it's glory connected this way.
In my experience, the HD 600 needs about double the power of your average headphone. So if you set volume past 50% with your current setup using an average headphone (32-70Ohm), you will need an amp. Contrary to what people say, most modern aftermarket sound cards (like mine) in the $90-$150 range can drive these to adequate levels. Specially new ones with built in headphone amps. So I suggest you get a sound card before considering an amp, this would give you a better DAC (most are 110dB SNR or more). That way if/when you get an amp, you wont need one with a DAC. This increases your options and will usually save you money.
If your going to be using a laptop/mobile device or all-in one PC, you will probably want an amp. I suggest to start with something portable, affordable and powerful, like the Fiio E07K (Andes). This amp has a DAC, but if you must use your devices DAC, simply leave volume under 70% on the device to avoid introducing more noise. Let the amp do the work, and you will be fine. That is what I do on my Fiio E11 with my Galaxy Nexus/Sansa Clip, and it sounds fine, with plenty of power to spare. I suggest the newer E07K model because it's more powerful and can be used as a desktop amp too (works while charging).
When comparing my X-FI to either the E11 or Bravo, sound seems to stay more neutral and clear (less noise) at higher volumes with the amps. But the volumes I need to push it to hear that difference is beyond what I consider safe for longer periods. Listening at safe levels, differences are negligible, even more so when comparing one amp to the other. If I was to get very analytical at higher volumes, I would say the X-FI has slightly heavy highs, the Bravo more mid heavy and warm, with the Fiio being the most flat. However, I hear a much larger improvement when going from my Galaxy Nexus+E11 to my X-FI alone, than going from the X-FI to X-FI + E11/Bravo. The main improvement is in sound stage and separation. This probably holds true for most cases going from a mobile to a desktop setup. I still consider the sub $100 amps worthwhile if you actually "need" more power, just don't expect it to improve the sound significantly, beyond adding volume. In my case, to make a worthwhile upgrade from my X-FI, I would need to spend $400+ on an amp.
For those who are into it, I hear great things about how receptive the HD 600 is to all forms of amplification. Some claim to hear big differences between amps or cables, even within the same price range. However, be careful not to fall victim to buying based on reviews at this stage. I say this because improvements at this point are largely dependent on ones tastes and/or analytic listening ability. People and their ears are not all created equal. In addition, reviews are based on the individuals unique setup, which could be drastically different than yours. Just like buying a new set of clothes, consider it a process to determine what fits you, at a price your comfortable with. You may have friends/family that own some good amps or hi-fi stereos, the older the better. Give those a try next time your there. If you actually hear a big improvement then you know it might be worth it for you to start shopping around. Go to a local store with your own source and headphones to test, or at least buy with a flexible return policy. Don't rush it, the more time you take, the happier you will be with the outcome.
I highly recommend this headphone for anyone who is considering spending this much, you will be hard pressed to find anything with a better blend of sound quality, comfort, style, and durability. The only other real contender is the Beyerdynamic DT880 600ohm. The 880 has better bass but requires allot more power and is not as modular, durable, or stylish (in my opinion). If you plan to ever use them away from your rig (but not in public), the HD 600 is a no brainer. You will be pleasantly surprised at how easy they are to drive. Worst case scenario you just need a sound card or a sub $100 amp like the Fiio E07k. If you are looking to get into amplification, this headphone is a great one to experiment with. 10/10 across the board for this puppy.