so let's see if i've got this straight (summarizing some info i've gathered) ... for ipod users, headphones won't need to go over the $300 mark, (maybe with exception of p7, but those extra 50 bucks are mostly high quality build/ design anyway) cuz those above need amps/dacs to bring out the music, and they also sound bad under 256 bitrate; maybe 320 depending on your ears.
iems should be cut at the $500 mark- (se535, w4, ue900, ie80, etc) while higher models don't necessarily need amping, a portable amp is recommended. they will bring out the bad points in recording/mastering/ and bitrates uder 256 or so quite easily, being detailed. for these higher end iems, a portable amp/quality music player with quality music is needed to justify their price.
conclusion: sell se535 at $400, and m50 at $150 (i live in korea)
buy dunu-dn1000 as iem $200, and p7 $400 as headphone (stuck between p7, nad viso hp50, kefm500, and maybe momentum/mdr1r/m100/k550, but will probably get p7)