Excellent IEMs

Overall a very solid headphone.  Can be used unamped, which may be a deciding factor for some.  HeadRoom got it right when it described a little "grain" in the presentation, but this headphone doesn't have many other faults.  At the same time, it doesn't have much to distinguish it from the increasingly good competitors.  If you are short on amps and want the Senn sound, then this is a solid choice.  Otherwise, go for the 600 or 650.

Headphones simply do not get better than this.  The first time I heard the O2 mk1 was at the First National Meet.  I was blown away.  I had no idea that headphones could sound like...that.  They simply melted away.  It some ways, they ruined that meet for me because they were among the first phones I heard.
 
Fast forward a few years and a few meets later and I decided that I had committed to enough money to mediocrity, and I finally pulled the trigger on a pair on the used market.  Amped with a KGSS DX, they are a splendid mixture of power and finesse.  "Liquidy" is a word I associate with them.  And there is not a single thing I would change about the sound signature.  They are, simply put, the best headphones with which I have spent a meaningful amount of time.
 
The O2 mk1 is demanding, though.  You will need to invest in a 'stat amp of some quality and feed it a decent source.  But that investment will yield sonic bliss.

The JH13 is not just the best IEM around, it's one of the best headphones around--period.  The impact, detail, speed, agility, and body of these phones are simply amazing.  The full-sized can I find myself comparing them to is my O2 mk1.  That's about the highest praise I can offer a headphone.  Jerry Harvey does not screw around.  The only cons are that it may take a couple of refits to get them dialed in (but this is worth it) and I sometime wish they had just a touch (and I mean a tiny bit) more bass.  But even that criticism seems to be waning as I get more accustomed to the sound signature.  (And I am consciously not ascribing this change in opinion to some ridiculous notion of "burn-in.")
 
And while some may find these very expensive, you get what you pay for.  Great sound; great customer service.  Well done JHA.  

A pair of headphones I wish I kept.  Great bass, excellent highs with the right equipment.  Scales with the best of equipment.  Everyone should own a pair at least once.  

LISTENED AT MANY MEETS
 
I never did get it about these phones.  I think they sound tinny and boring.  The only time I have ever heard them sound somewhat decent has been out of the big HeadRoom amps.  There's something to that combo.  Otherwise a real snore.

BORROWED FROM A FELLOW MEMBER
 
Wow, did I want to love these headphones.  And I just don't.  They're fine.  They don't do anything horribly wrong.  But the also don't do anything extraordinary, and for the price being charged, they should.  I think the HD800 is better.  However, it is a very comfortable phone and the build quality is superb.  Just a bit blah to me.

An expensive, technically proficient headphone that has no soul.  Does mate well with the Luxman P-1 or P1-u, but at that point, why not go electrostatic, which is what these are trying to be in the first place.  Kudos to Senn for innovation, but these are just too steely for my tastes.

A bass lover's phone for sure.  Can be fun with the right music.  But the bass is of the one-note "whump" variety and that gets boring.  Still, can be good with rock.  I've noticed some pretty sucked out mids, though, so vocals suffer.  And for a bass-head phone, the highs can get pretty brittle.  Not at all a balanced presentation, but that doesn't mean it can't be fun.  Everyone should give these a try.  And they're built like a tank.

DISCLOSURE: I received a loaner D100 as part of the Neko Audio D100 loaner program.  Wes Miaw, the man behind Neko Audio put together the loaner program.  All outgoing shipping was at my expense.  The loan was not contingent upon a positive review.  However, Mr. Miaw did ask if I would post my impressions (good or bad).
 
The D100 is an unassuming DAC.  A black box with a silver knob input selector in the middle and the ubiquitous blue lights for power and signal lock.  The unit is small and unobtrusive, and while it isn't high fashion, it is well-built and utilitarian.
 
I'll leave the technical details to others, but it is my understanding that Wes chose to forego some of the bells and whistles for premium parts and execution.  Good decision.  With the D100, Neko Audio appears to have sought a well-rounded sound.  It is not the last word in detail.  Good.  I've had it with brittle, shrill DACs, which, frankly, at this price point is what you get when a DAC manufacturer goes for "detail."  So instead of the sparkly highs, the D100 gives sumptuous mids and a bit of bass kick that I find very musically satisfying. 
 
To put this in context, the D100 doesn't sound "gray" or boring like the Bryston BDA-1 does. Instead, the D100 has that sweet sound that reminds me of the Electrocompaniet ECD-1 (one of my favorite DACs out there). And the D100 is one of the few new DACs that I've heard that isn't afraid of presenting plenty of bass.  And I suspect there's a little mid-bass hump there that contributes a bit to the euphonic sound signature that I perceived.     
 
Now, does all this mean it's just a fun DAC and therefore relegated to Mid-Fi?  Maybe.  But if this is mid-fi, then that's where I want to be.  If you're in the market for a DAC for $1000 - $1500, you ower it to yourself to investigate the D100.  It's just a really well sorted DAC.
 
 
Associated equipment:
 
Phones: O2 mk1, Grado HF-2, JH13
Amps: Beta 22, KGSS DX
Transport: iMac optical out playing ALAC