If you store your files in the Apple Loseless format it won't make any difference between USB or Airport, but if you don't use any file compression, then the USB connect has the potential for better performance since the Airport will convert everything to Apple Loseless.
Which way to go? Airport Express or USB interface
I'm thinking about creating a computer stereo with my Mac G4 and some set of devices, including an SS integrated amp. I've heard from a few computer tekkies and an audiophile friend, read some forums on Audiogon, and it's hard to fathom which means might provide best fidelity--the Airport Express wireless method or the USB audio interface method. Some say the source files are most important, but I can save data according to recommendation. It is the linkage/transfer system that concerns me--USB (16-bit or 24-bit) or wireless. I can attach (or not attach) an outboard DAC to either, then run an analog in to my integrated amp--correct?