I downloaded the Vox music player to my iMac today. I set the Vox player to output at an upsampled rate of 96KHz and set the iMac to output the 96KHz signal through the optical output to an MSB DAC feeding a JDS labs O2 amp feeding VModa M80s.
I've listened to MP3 cuts from Adele's 21, Michael Tilson Thomas and the San Francisco Symphony Orchestra's performance of Mahler's Symphony #6, a few Flac formatted cuts from an HD Tracks purchase, and some MP3 cuts from Mark Knopfler's Shangri-la album.
I've listened to all this music dozens of times. The sound I'm getting from this setup is the best I've ever heard. I'm hearing more of the music and not finding a single aspect I'd improve.
Now, of course, that doesn't mean it's the best. I'm sure there's better. But for now, I'm quite content.