For many of us who have not heard all of these combos, we tend to go with what we know, which is probably not the ultimate best combo. So our votes may be meaningless and inaccurate. Unless of course, the supposed expensivo gear is simply different sounding rather than better. Of the phones I own, I am hesitant to submit the Sennheiser HD600 because I find them simply too veiled and laid back, compared to the AKGK501 and the Grado SR325. Or, to put it more accurately, it's colorations are not quite my cup of tea. When I listen to the K501 with the RA-1 amp, I feel like I am seated midway back in a concert hall, listening to an actual performance (especially with classical music).
But again, having not heard the best Stax, or Orpheus, nor the Holmes-Powell or EAR amps, I have no idea what the ultimate headphone experience might be.