The 125i is certainly the rarest model on these forums, I also suspect that it is the least popular seller
in the SR series, most people jump from the SR60/80i straight up to the 225/325i.
Only difference is that the SR80i has a standard copper voice coil while the SR125i gets the
high quality UHLPC copper voice coil. Both retain the standard headphone cable.
225i+ gets both UHLPC in the voice coil and in the cable.