Pros: Sound quality, accurate reproduction, comfortable, price
Cons: Not portable, fugly
Reading reviews is one thing, as we all have our own subjective opinions, but when something receives a majority of praise, I think it's worth a try.
When the 681's arrived, I wasn't impressed with the packaging, but they looked as I expected them to look. They feel pretty durable and the look is retro, I can't see myself taking these outside since they don't fold up and they are kind of fugly.
Looks aside, the sound from these is nothing short of amazing.
I'm running them out of my Dell Inspiron 530 desktop (Core 2 Quad) with a Behringer UCA222 in the signal path. The files are all WAV or FLAC.
The 681's are very easy to drive, I don't feel the need to hook up my Fiio E05 or my Fiio E11. I'm getting plenty of volume, with room to spare, from the desktop.
I've been listening to a very wide variety of music and the 681's are working very well with everything. Acoustic, Folk, Jazz, Blues, Rock, Progressive Metal, Industrial, Hip Hop, Rap, they all sound really amazing on these Headphones.
I'm really glad I took a chance on these.
Compared to other Headphones that are in the same bracket, like the Panasonic RP-HTF600-S Stereo Headphones and the Monoprice 8323, I believe they aren't in the same league, as far as performance. I realize the 681's are a semi-open design, but so are the HTF600's. I'm not putting the 8323's or the HTF600's down, as they are very good headphones in their own right, but I overwhelmingly prefer the sound of the 681's.
The 8323 and the HTF600's are more portable but the Panasonic's don't really fold either but the cups rotate a little, whereas the 8323's fold up in the smallest portable package of the three.
So, the details the 681's produce are spot on, to me. I don't have a higher end set up to compare them to, as the only other headphones I own are Sennheiser PX100's, PX200's, and Audio-Technica ATH-M50's.
Out of all those sets, I really prefer the 681's. I don't find they are lacking in any aspect. The bass is deep, fast, and tight. The midrange is fabulous, the vocals and instruments sound SO good. I don't feel the treble is too bright or forward or harsh. These headphones seem to reproduce exactly what you feed them, and that is no small feat.
Since they are "semi-open" the sound isn't contained, so others can hear what you are listening to and the sound from the surrounding environment creeps in without much resistance. This is another reason I don't see the 681's as ideal for use on a commute or in an office environment, unless you need to be aware of your surroundings. I don't think you have to crank the volume up much to get a really decent level of sound with these either.
I do appreciate the reviews on equipment submitted by everyone else on head-fi. This is a great resource and it was very helpful in my search for some decent setups.
As with anything else, this is just my opinion of the 681's. Your mileage may vary.