There's been a lot of buzz about "HD audio" lately — some even rumored that it would be included in the iPhone 6 and iPhone 6 Plus — but the dirty little music secret is this: Humans can't appreciate the difference if all you're bringing to the track is more bits. Dave Hamilton does a great job breaking it down on MacObserver:
This difference between 16-bit/44.1kHz audio and anything greater than that has been tested (a lot... in double-blind tests) and we have yet to find any human that can reliably notice that difference. Bit depths greater than 16 bits and sample rates above 44.1kHz simply don't matter as long as the data is converted properly (and our ability to do that conversion has improved substantially since those very first CDs were released at the dawn of the digital music era).
The whole piece is a terrific, so give it a read.
I've spoken to many people knowledgeable in audio and codecs and they've all said the same thing as Dave. I'd go so far as to suggest the only valuable thing to come out of the entire 'HD audio' movement is the remastering that's being done to prepare for it. Many of those works were in dire need of it, and the marketing gave labels and studios and excuse to do it. (Even if those new masters would sound just as great at 16-bit/44.1kHz...)