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?