Thanks, and I would also like to ask if my Fiio E6 amp connected to my ipod would make a worthy improvement in sound for either the R50 or the HF5 for the inconvenience of having that extra bit of stuff to carry around and the slightly annoying square bulge coming out of my pocket :P
Only you can make that decision. Do you already have the E6? Are you using the LOD cable? I would guess that it would make a bit of a difference, given the lower output impedance. I would consider the E5 over the E6, if you haven't bought one yet.