oops! Wrong forum
Moderator will probably move you over to portable devices.
In a nutshell, the creme de la creme of PCDPs per reviewers on this board is an older Sony design called the D25. Available at eBay for roughly $45. Main reason cited for superiority is power output (can even drive Senn 580s well w/o amp) and general musical nature of sound reproduction (though higher end of treble range has been critiqued by a few.) Also, the D25 has a short battery life and minimal to no skip protection and is also largish and bulky.
Amongst more modern designs, Panas are generally liked better than Sonys. The SL 470 and 570 are usually described as the best of the current bunch. If you already have the power output solved (with your amp and easily driven V6s) than you have a lot of options as Panas are usually cited as being better phones for reasons of power output rather than actual sound, so you could go with either higher end Sonys or Panasonics based on other concerns like features, size and weight etc.
I am summarizing my own post searches here; I own a Sony DFJ61 which I bought before looking on headfi. It works just fine, sounds OK, and lasts forever on 2 batteries. But no one else here seems to have much of an opinion on it one way or the other... Hopefully you will get other responses!