I'm currently running my MBP with iTunes and Amarra, with an Audio-GD FUN currently en route to my residence. Been burning in a new pair of AKG k701s this week (With pink noise, and silences in between so the tweeters can rest), and today i decided to take them for a test run.
Playing Melody Gardot's "Our Love Is Easy" in lossless format, I discovered some serious distortion at higher frequencies that I figured were due to the file itself, since I tried the same file on my MBP and iPod, through different systems. Today I downloaded the demo version of Channel D's Pure Music player, and set my sample rate to 96khz as per the instructions in the guide. Once I enabled upsampling, it seemed as though all the distortion vanished!
Can someone explain if the sudden lack of distortion at higher frequencies is due to the upsampling or something else unbeknownst to this humble audio newb?