if you get an USB headsets, then you only able to use with your pc

if you get the 3.5mm headset, at least you can use with your pc, mp3 player, phone n bla bla bla
future investment with the soundcards still able to use it with the current headset what

isn`t "headset" same as the headphone?
or headset is the headphone came with the mic? lol
sorry for my dumbness
SR60 would be much more better compare with the PX100-II
comfortness, build quality i would say is really above the PX100-II

u could try search the following headphone as well :
Beyerdynamic DT231 PRO
AKG K420
denon AH-D501
Audio Technica T500, AD300
Shure SRH240, SRH440
Sennheiser HD408
Koss Portapro
definitely increase SQ 

AKG GHS1