I have those original Sloth 701's and this headphone remains ahead of my other 701's ... apparently because these are fully burnt in. But my other 701's are starting to come around. I now want to pass on some thoughts I have from comparing the 701's to my senn 600's these past several weeks. I have some observations that are a little different than most. In short, I think the varience in some of the opinions has to do with, first, the amp being used, and secondly, the overall system synergy.
The 701 likes current. If I use my mpx3's with the lower power 6/12sn7 tubes the headphone can struggle with music with demanding bass passages or high dynamic peaks. I defintely hear some harshness and lack of resolution when the amp cant feed the 701 enough current ... and lots of uncontrolled bass. Now ... pop in some higher output 5687 or 6bl7gt output tubes and these issues disappear completely. The bass is extremely potent and tight with the 5687 tubes. There is no harshness to the upper registers and dynamics are fully developed. This headphone needs an amp that can supply current and do so without harshness ... or the 701 will let you know.
Now move on to sources. Again, the better the source the more resolving and refined the 701's become. Going from the sacdmods 555es to the E5 results in less bass, more brightness and a somewhat diffuse soundstage. Some of the problems I thought I heard with the 701, at times, has been the headphone simply passing on the flaws present in my lesser source ... and the recording. Source inadequacies will be revealed in their full glory by the 701's ... particualrly in the treble. Some of the positive comments about the 650's treble is, IMO, simply that the 650 doesnt pass on all the information the 701 can ... resulting in better perceived performance with poorer recordings. I came to this same conclusion at first. But once I spent more time with recordings having well recorded treble (cymbals especially) ... I changed my opinion.
In addition, the system matching itself seems vitally important with this headphone. I have found the setup I use with my senn 600/ cardas is not optimal for the 701. Once I made changes to optimize the 701 the results were atleast equal to the 600 ... and in certain ways clearly better. I caution you against dropping the headphone in the exact setup as your senn/ beyer or whatever and expecting the 701 to excell. Cables, tubes and recordings that bring out the best in my senn 600's dont work AS WELL with the 701's. I am in the position I can optimize for both and thats probably why I struggle to find a favorite ... at their best both are exceptional headphones. But most of you will have one amp and no extra cables etc ... and you will probably prefer the headphone that mates best with what you have.
After a couple days of marathon listening and comparing ... the 701's just do everything well. The senns remain the 701's equal in musicality. But I continue to hear the 600's minor flaws where I just cant find anything to criticize with the 701's.
I also caution you to make sure your listening levels are reasonably well matched when you compare these two. I find it nearly impossible to set the 701's correct listening level by ear. If the level of the 701 is to high I think they are to bright. If the level is to low with the 701's the bass recedes. Everytime I find something I am ready to downgrade the 701 for ... I find its been the setup ... and often the volume level. Once I level match the 701 to the correct level I prefer there are no issues. But the headphone is so well balanced there are no cues when I have the listening level slightly off.
As to that level ... I seem to prefer the 701's with less volume than the senns. The clearer more open treble is better at lower volumes where the senns can sound to dark, plus there is plenty of bass, unless I set the volume to low. I set the senns just loud enough there is a good sense of life to the treble. I usually can tell if the senns level is to high immediately because the bass sounds to congested. The 701 is much harder to figure out. I can listen for a quite awhile before I am bothered because the 701 is so well balanced.
Level matching both of these headphones to the same volume results in one being favored over the other. I have come to the conclusion comparing them as apples and apples is pointless. I have found setting up each headphone at their best, and then comparing, is the best way to see which one I will ultimately prefer. the ultimate levelas are close ... but I like the 701's 1-2db lower depending on the recording quality.
At this juncture if I had to pick one I would take the 701 solely because its more comfortable to me. I am thrilled with the sound quality of either headphone. But there is something about the senns presentation, that while not as accurate, is more musical and slightly less fatiguing with some music ... and they will be staying. The 701 doesnt hide recording flaws the way the senns sometimes do. But the 701 doesnt make flaws worse than they are ... and the 701's resolution lets me understand the flaw is often a recording artifact ... which somehow makes the flaw less bothersome.
Anyway, I wanted to give everyone a slightly more obcessive view of the 701.
I have been comparing these headphones for weeks now so I may as well pass on my thoughts.