I am currently using Klipsch X10 + iPhone 4S. The X10 quite surprised me that I don't need an amp for it, the quality turns out pretty good, as wells as pairing the X10 with my thinkpad laptop.
Now I am thinking of getting a JH13. The only thing I concern about is that if iPhone 4S can drive the JH13 w/o an amp well.
English is not my first language, so if you cannot clearly get what I wrote above, please let me know:) I'll respond asap!