Just got myself a pair of these bad boys and I'm loving them, they are helping me find time to listen that just didn't exist with clumsy cans and finnicky IEMs. However anyone saying the PX100-ii are the technical equals of the HD598 needs to get their Pink Floyd game on, or maybe listen to some orchestral music in flac to hear the very real advantages in tonal balance, soundstage, and detail retrieval that the HD598 has over the portables. If this kind of music isn't in your diet, more power to you, because the PX100-ii sound killer with just about everything else, and have a really engaging, spacious sound for something so tiny, but they do lose ground to higher models when it comes to more advanced recordings. To me, the strength of the PX100-ii is that it gives something pretty darn close to full-size open can sound in a package that I can take anywhere, and even lets me get in little "sneaky" listening sessions at times they normally wouldn't be possible, like while I'm filling up gas in my car, or when my girlfriend goes to the bathroom while shopping and I'm just standing there waiting. Unlike IEMs and most closed headphones, the PX100 has some serious soundstage for a tiny package (at least depth, if not width), which allows it to sound much more natural/speaker-like than most of the alternatives. And its not as much of a pain to put on/take off as IEMs, which makes quick little sessions much less of a hassle. That, along with its presentation, are why my UM3X, X10, and SE215 are currently collecting dust.
