Thanks for the responses guys!
I sorta figured if there was any loss that it probably wouldn't be audible with my headphones/system. And yes, I'm not looking at a long extension. As owners of the PX100 are aware, the cable is somewhat short, of course it's fine for portable needs though. Anyway, because I get clearer audio out of the back of my PC, I want to plug my PX100s in back there. It causes the wire to be quite tight due to the distance. That's why I asked about extension cables. I think I'm just going to wait until the FiiO E5 amp and use the small extension cable it comes with. Should solve my distance problem, no amp out of the back jack problem, and any potential issue with a long extension cable since the included cables with the E5 are quite short.
Thanks again!