Well it's been over a half year since I've had both the K701 paired with the E9/E7. I thought I'd give my thoughts on the headphone, and to a lesser extent the wunder-amp Fiio has cooked up. As far as the headphones go, I bought my set used from MadlustEnvy back sometime in late '10, when I cannot be sure as I am too lazy, and/or drunk to look up the date on Paypal at the moment. I am unsure of the amount of burn-in given to them at the time that I received them. Suffice to say that in the short time I have had this pair in my hands (Serial #22512) if you were wondering the changes I have noticed have been dramatic, to say the least. When I first received the headphones they were sibilant and harsh, to an extreme on any recording that wasn't perfect. At first I was slightly disappointed, but I chalk that up to coming from the extremely bass-heavy Klipsch S4 IEM. They were enjoyable, especially with guitar based music, whether it be folk or metal; and by metal I mean all types: from the well produced prog and thrash metal to the "recorded in the carcass of a dead rat in a prison cell of a castle" black metal", the treble emphasis, while fatiguing added energy like you would believe to these recordings. As the phones burned in that treble emphasis chilled out, as well as the wonky mids, which upon first listen made pretty much any jazz recording sound like utter rubbish, have experienced an absolute 180. Anywho, I feel as if I'm saying nothing in a long paragraph that will only infuriate other readers who have been interested in the headphone so far. Given an extreme amount of burn-in, and I do mean extreme. These phones took at least half a year of constant (i.e. 4-7 hours constant listening daily) to settle in to their final state, at least driven by the powerful albeit a bit sloppy Fiio E9. As of now, the K701 will still be bass-light if you are bass head. But, to say that the bass is nonexistent is a fallacy, it is there, it doesn't thump until your head aches but it is there. The treble has cooled down tremendously, which is a relief to me, as many recordings that I listen to are poorly recorded and treble heavy. When I first received the K701 I couldn't listen to Mingus' Mingus, Mingus, Mingus, Mingus, Mingus or Darkthrone's A Blaze In The Northern Sky without having my ears bleed afterwards. After burn-in this is no longer an issue, the wonderful PrAT is still there, and the phones are indeed quick as all get out, but they are not near as harsh and thin as when I got them.
Now onto the contentious spot, the Mids. Oh boy there is no in between when it comes to the midrange with this phone. There are those who embrace the weird, thin, honkiness that these phones have until almost 1k hours of burn-in, and then there are those who find the honkiness and the the thinness of the Mids as a total deal breaker. If you dislike the Mids of the K701 I have no gripe with you, as they are admittedly thin and somewhat cold and unreal sounding. But, in my case I've made my amends that no headphones can give the live experience through the limited... er tech that is in headphones at this moment. Mind you that I'm a tad buzzed and have not the funds to invest in a Stax Omega system, so this *is* a personal experience. If you have heard other competing headphones (i.e. DT880, HD600/650) I commend you for having the financial security to indulge your tastes; but seeing as I am a lowly temp working with a budget amp and a notoriously picky headphone that is either loved or hated I hope you will forgive me.
So comes the "Too long, didn't read" portion of my erm, findings. I found the K701 to be perfect with bass in my opinion, it isn't too overbearing, but it also isn't totally disregarded in exchange for treble. The mids, even with extensive burn in of both my amp and headphones are still slightly wonky and unnatural. I don't think the mids will become realistic until I invest in amp that is befit a headphone of this caliber. The biggest change is the treble, if you may pardon my French, holy crap! This is the most noticeable change with burn in. The highs smooth out, where they used to be sibilant and painful they, say they were at 11 (to borrow a Spinal Tap reference), now they would be at a 7. They are much more in tune with the rest of the frequency spectrum. And while poorly recorded music is still noticeable, it does not sound as near as bad with burn in.
If you disagree please crucify me and leave me for dead.
Edit: Hehe I said "pickly"
