These headphones are quite good, and have really great highs.  They are an improvement over the SR-80i, with a more balanced and bright sound with better articulation.  For the money, they are quite good.  
 
These headphones do need to be broken in a bit.  The highs start off a little harsh and tinny, but end up pronounced, but more balanced.  They also need to be amped to get the full sound.  Without an amp, they are dead.  With an amp, they are brought alive, and have more bass and highs.
 
The place where the SR-125i's really shine is in the mids and highs.  They are bright but accurate.  and they have a little punch that really adds to music.  They also have good direction and and have a very bright sound.
 
The bass, however, is lacking.  It is there, but more for support than the main exhibition.  It retains a very crisp sound and also has a little punch to make it stand out. This sounds really good depending on what type of music is being played.  Music from the band This Town Needs Guns (a math rock band) sounds incredible on them.  
 
Soundstage is another  point to consider.  Its pretty much not there.  This makes the SR125 much better for certain  types of music compared to others.  They really sing on most rock music, but when it comes to acoustic music, like Sun Kil Moon, a lot is lost in translation.  That type of music really begs for a large soundstage, which the 125's don't have.
 
The worst thing about these headphones is the fact that they are not very comfortable at all.  The headband really digs in after a short while listening.  I have found that this discomfort can be overcome by placing a sock between the headband and my head.  It makes the headphones much more enjoyable, but looks rather odd.
 
I got the chance to compare these headphones to the Grados Labs SR-80i, and I prefer the SR-125i greatly.  The SR-125's seem much brighter and better balanced than the 80i, 
The main reason I purchased these headphones is to act as a counterpoint to my Audio Technica ATH-A700s, which have a massive soundstage.
 
Something to note: The SR-125i's have a large, thick cable and a 1/4 inch connector, so a 1/4 inch to 3.5mm connector is needed.

 
I have had these headphones for four months now, and they are great.  They are relatively inexpensive (at around $120 on amazon), and have a very good balanced sound. 
 
The frequency response is pretty good, but they lack bass.  With amplification (I am using the fiio e7 e9 combo), the bass becomes more prominent and the sound is much fuller than unamplified.  While amps improve the sound, these headphones are easy to drive and still retain the soundstage, even while listening at low volumes. 
 
The biggest plus to these headphones is that the soundstage on these headphones is massive.  It sounds like the music is coming from the tip of the nose.  It really brings live performances and acoustic music alive.  These headphones lend themselves well to classical music, but they are also good for most music.  I also listened to some vinyl on them, and they sound great. 
 
They are also good monitoring headphones for recording music, as they are accurate. 
 
They are also very comfortable and do not clamp down at all, making listening to them for long periods of time enjoyable. 
 
The main con of these headphones is the lack of bass, but this lends itself well to music where having booming bass is not as important. 
 
Overall these are very good headphones, not incredible, but a very stable place to start with audiophile headphones. 
 
I had the opportunity to compare these headphones to the AKG 702s, and they actually sound quite similar.  The AKGs have more separation between instruments, but the Audio Technica ATH A700’s have a much larger soundstage.  The AKG’s also take much more power to drive them, and really need to be amped to get a good sound.  Unlike the Audio Technica’s, where sound just gets improved by the amp, and it is not required.