Curious to find any electronic mods for the Airport Express, I ran across this tip for improved iTunes fidelity on a Mac: switch your MIDI controls to 24 bits.
On a Mac, launch the Audio MIDI Setup.app from your Utilities folder. Change the Audio Output controls on the Audio Devices tab to 88200.0 Hz/2ch-24bit for all sources as in the screen shot. You can actually switch the settings while iTunes is playing for A/B comparisons.
Tonight, I’ll apply this to the Mac Mini and see if it carries through to the Airport Express. I think my Onkyo will display the bit rate it is receiving from its digital inputs.
I’ll post another listening test if the upsampling makes any difference to the sound. The Pioneer DV-47ai is upsampling to 24 bits so I’m hoping the gap between Airtunes and CD closes further.
As for the mods I found, audiophile tweakers have gutted the Airport Express’s analog/digital output and replaced it with a digital coax pig-tail with silver Eichmann Bullet Plugs, hacked the USB port to feed an external USB DAC and upgraded the power supply. Nothing simple enough for me to try, I’ll just keep the little plastic case uncracked.