I use mine with Violectric Amp and Dac and they really come alive with the extra power and flac files.

I will put that on the list of future things to try. I have also been told that the Bottlehead Crack with speedball is worth my time as well!

I had mine paired with my WA6 and it was one of the best pairings I've ever heard. I wish I'd of kept them. 

I should review them myself.

Thanks for the comps! The 558 were my "toe in the water" of quality headphones, and I've always wondered if I should have tried the 600 instead of trying out planars (ended up with the 400i).
 
Would you say the soundstage for the 600 was noticeably bigger than the 558? 

The HD600 are iconic for a reason. Well amped they are simply excellent and neutral; I think everyone should have a listen, especially when first starting into the headphone hobby, just to understand what a "neutral"  sound signature is- the HD600 is the generally accepted reference.

@mike138 These are a no-go if you are interested in soundstage. Personally for that I would say HD700, or Fidelio X2. HD650 is a much closer sound to the HD558 than those, and coulkd also be a good option.

Nice review. I started my audiophile hobby with them, sold them, went for planars from Audeze to Hifimans, to other dynamics from Beyer and Denon ended up with HD 600 again. The only other headphones that are worth having along with these are the 800/800S and the LCD 3 for me.

Could you also add a 600 vs 650 comparison section? Personally, I liked them both but the 800S killed them.

I will do my best, but to be fair, I didn't get to try the HD650 with the Polaris amp, so it is not really a fair fight.

Also, if it interests you, I wrote a full review of the HD650: http://www.head-fi.org/products/sennheiser-hd-650-headphones/reviews/16145

I once asked a HF member here with an awesome collection of high end cans inc Stax planars and just about every flagship model why he still had the Senn HD 600 and not to my surprise as I also own them he stated that they were simply the most natural sounding of all his collection and got lotsa listening time
Be aware that they do scale up nicely with better Amps
Interesting to note these cans have been around for yrs
I think Senn still makes them??

Nice review @snapacap! Thanks for sharing! 

Best most neutral headphones I ever had. You need nothing more then hd600 in your life.
Powering with objective 2 with great results. Needs nothing more. Schiit Valhalla 2 just hair better at 4x pricetag.

I had a pretty hard time trying to beat the HD600 with higher gear. Only the Lcd-3 paired with a high end amp got me to the next level, and that's something to say about the old cheap HD600.

Great review, after two HD650s (all great) and now an HD700, I think I will have to try out the HD600 next. 

Good review, "natural" seems to be the word I read consistently when describing the HD 600, you just made me take off my planars and put on my HD 600 to listen "The Veldt" by deadmau5.  So lovely!

HD600 and  HD 25-13 II had to be two of most iconic neutral headphones reference for Sennheiser.
I believed if HD255-13II ,which is 600ohm headphone, weren't being discontinued. It would have hd600's reference status it had today.
I have both HD600 and HD650, Both seem to be a different beast,at least,for me.  Definitely keeping both.

hey @Vekk , HD25-II absolutely is a reference classic. Reference for so many reasons, if not for its own characteristics familiar to thousands on engineers, producers, DJs, and head-fiers. 

I gave mine to my bro, had the Amperiors for a while (a little sweater overall, and not the same reference). I did find an upgrade/replacement to the HD25 for the same purposes, and that is the MDR-7520. Same very flat mid-range, but much more accurate and extended in the bass and treble range. Top-notch durability too. Still, HD25, light, durable, pretty comfy for on-ear, and indestructible (I had a pair lend to a friend for a several year SE asia tour, where they survived motorcycle crash, fire, and rain!)

Use mu 600/650 with Meier Corda Mk2 (purch'd 2004, and extensively modded later) or a Tangent PPA v2 (diy amp). Also tried with HeadRoom Max. All these amps are solid-state jobs. Waiting to build a tube amp as I've heard the Senn 600/650 REALLY come alive with valve sound