Despite only having listened to the Portapro and the PX100-II for a few seconds in electronics shops here in Japan, I would say that if I were you I would go for the PX100-II. I have owned the older PX100 for over 1 year and I appreciate them more and more.
I did some cross listening at the electronics store and compared the Portapro, PX100-II and the AKG K420 (which I also own) and to me the Portapro is too much "in your face" and my ears were not really given much room to breathe. The PX100 are almost the opposite (I do not remember the exact sound signature of the PX100-II so I compare to the PX100), quite airy and not as forward in the highs. To me it sounds like it reproduces more details than the AKG K420, which to me sound a bit like the Portapro except a bit less "in your face". But some people think that the PX100 sounds too "veiled", probably because of its treble roll off.
I have read comparisons between the Portapro and the PX100 saying that if you want to dig the music, the Portapro is the best good choice and if you want to listen to the music the PX100 is the best good choice.
It also depends on the music you listen to and your source. If your source is bright sounding, the highs might be too much with the Portapro. Then the PX100-II are better. If your source is not very bright sounding, the Portapros might be better.
About the PX100-II you could always search the forums. I remember reading about it.
Here's a link to another site where they talk about the PX100-II.
Here's an older thread from Head-fi:
PX100 vs Portapro
A short review of the PX100-II by someone who has owned the PX100.