Highest Possible Sound Quality from iTunes

[Seb310]

Hello.
Concerning the sound quality with itunes : considering Itunes as just a "file manager", Audirvana (or whatever) as "transmitter" in bit perfect mode, and considering an asynchronous transmission to the Dev (managing the DAC), where (or when) could occurs any loss in the data ? And by the way, what can explain a difference between two asynchronous methods (ie AIR3 and USB) ?

Thanks for your lignting