If you are using iTunes for playback it does not auto switch sample rates. You have to manually change to the 24/96. That's why a lot of people use a third party playback software like Audivrana and Pure Music (Mac) or dbPoweramp (Windows) for playback because they will auto switch.
HDTRACKS sample rate
I downloaded the free sample from HD TRACKS, which has a sample rate of 24/96 to see what the fuss is about. When playing it from my laptop to my Marantz SA8004 USB input the sample rate reads 16/44.1 The Marantz is supposed to accept inputs up to 24/192. Anyone know why it's only playing at the sample rate of 44.1?