Digital Formats

Wondering if there are any real differences in digital players. For instance I currently run a wadia 170I into a Theta dac. Would there be any real sonic differences in going to a high Rez music player such as the Sony HAP-Z1ES or any of the other music servers currently out?
Yes. Higher sample and bit rates when used throughout the recording/manufacturing chain will produce more accurate sound reproduction.
"Is there any truth to the whole hi Rez business?"

Absolutely. There's plenty of places that sell hi rez music.