After reading the new Headroom review of the PX200 I tried them out again, concentrating on the bass. I found the bass quite respectable, even after shifting them around on my head quite a bit. I don't know if it's the burn in, but my impression has changed quite a bit from when I first got them and wrote a review saying that the bass was lacking ("an extension of the midrange" I believe was my phrase).
I think the bass on the KSC-35 is somewhat exaggerated, but otherwise I prefer their sound to the PX200. I find the PX100 darker sounding than the KSC-35 and am not sure I would recommend them as an alternative. The open, slightly emphasized highs of the KSC-35 are one of their likeable qualities for me, and the PX100s certainly don't sound that way to me.
Overall, I give the nod to the PX200 for the main reason that I've had rattle/grattle problems with two pairs of KSC-35s, so I would consider durability a real weakness. And has been mentioned above, they offer no isolation.