I did a shootout between playback software a few years ago and was shocked at the results. Playback software SIGNIFICANTLY alters the sound you get out of your files. I was running my Dell lappy > EMI 2|6 > dCS Delius at 24/96, and some playback apps caused the Delius to lose lock if I had the DAC in "narrow mode." Narrow mode was better sounding on the Delius, and related to the PLL lock that it would perform on the incoming datastream. You could switch it to "wide mode" for jittery sources, but this somewhat softened and diffused the soundfield to a negative degree, as I recall.
Anyway, even among the apps that I could get to lock with "narrow" I found a wide variability in the sound quality.
I am sorry I don't have the results of my test, but I specifically recall WinAmp was the WORST sounding alternative, and either Wavelab or CoolEdit was the best (I am thinking it was CoolEdit... don't remember). Since all my 24/96 files were very large, I didn't care too much that I had to get up and re-load the tune every hour or so. Now this was when I was *really* listening... If I was just putting on background tunes WinAmp was fine.
FWIW WinAmp will definitely output 24 bit.