Well yes all music will be better out of a home stand alone player VS a PCDP, but it is always simple, Monday morning QB'g the guy into buying another $1000 worth of gear as the easy suggestion.. lets try and work this guy a solution based on his thread and qualitative feedback,
I used to own the 650, and found it power hungry but quite happy with the synergy that my D-25 produced out the strong Headphone Output..
There was a D-25 for sale in the forum just the other day, I would check this out as a sub $150 transport, as this is not a truly portable unit, its sonics are some of the best of the vintage Sonys, and the headphone output is strong enough to push any Senns you can throw at it, I have tried the K 701's and they sound pretty good too on the unit, but have not A/B'd the Beyers with the D-25...
Easily drives Senns and is every bit as good as a player up to around $250. The Discman route to a transportable source will not leave you broke like a Nad, Rotel, Meridian, Cambridge, Marantz/Denon, or Arcam, and may give you useful insight about your preferences in timbre, soundstage, and imaging, that will behoove you in the future, in the event of an upgrade, or eventual swapping out of gear..
Getting into a <$1000 player if you are not rolling in cashola is a so-so idea, IMO...as from personal experience, the REALLY $$$ ones fail as easily/often as the Vintage portables..except you cry and swear longer when the big ones conk on you
I find great use with my Vintage units and bust out the BM1 DAC if I need some extra smoothness..but personally, a standalone transport will destroy any portable in terms of depth of sound, sonics, total range in dynamics, porper current/IMP, and of course overall transparency/musicality.
The D-25 is a handy transport, just recently sold my spare unit (and the Senns that I used with it, along the amp) but those all can be found..
ironically the RA-1 amp that does not mate with much besides Grado, matches the 580/600/650 rather well, and not just the HG model, fyi
If going the Stand Alone route , try audiogon or FS forum maybe eBay..
(try and find an old D500se from Cambridge down the road if possible, not a bad player if you uprade the OEM power supply)
Hope this helps,