Great review, spot on and well articulated. For my needs which are primarily portable, the M-100 is my favorite headphone and pairs nicely with inexpensive portable amps. As I admittedly listen to a great deal of popular music, I can't imagine a more enjoyable sound signature and presentation for that genre. Also, thanks for the Iphone 5 comparison. Based on your comments, I am in no rush to upgrade my Iphone 4.

Wow, thank you for providing specific examples for tracks between the HD25-i-ii and the M-100. I'm sure there are some users out there who are looking for a comparison between the two.
For the M-100's soundstage, you mention that it's "transparent". Could you elaborate more about what a "transparent" soundstage is? I don't believe I've heard the term used to describe a soundstage before as most people talk about its width, depth, and sometimes height (I don't think height is really applicable for traditional stereo recordings).

Excelent review. Thanks.

Thanks so much! Excellent, in depth.

Transparent soundstage in my mind means the sound seemed to come from everywhere else except from two little speakers next to my ears. It didn't have the typical "closed headphone or speaker in a small cabinet" coloration to the midrange that many closed headphones have.