Just a link to a long and neat article over at Tom's Hardware (no not that Tom, another Tom).

http://www.tomshardware.com/reviews/high-end-pc-audio,3733.html

Unfortunately they stuck to headphones for their listening tests. Realistically they should have used loudspeakers, one brand same all the way through, as most 'hifi' audio folk don't listen with headphones exclusively, but inevitably we know that the audiosnobs out there will simply rely on the ol' faithful standby "but that brand of speaker isn't as good resolution as X brand of speaker which is why they didn't hear any difference".

In any event, they did address this in their blind listening test methods, along with the fact that their sources were not being instantaneously switched.
_________________________
"Those who preach the myths of audio are ignorant of truth."