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.
So the new Sony HI REZ player is dependent on one loading HI REZ music onto it then to play back HI REZ? If my music is ripped in wav and apple lossless then I would get no benefit in going from my current set up of a wadia I70I into my Theta Dac to the Sony HAP Z1?