Yes, Foobar, with WASAPI(or Kernal Streaming) plug-in is a must have on pc! It bypasses all that Kmixer stuff in Windows, and delivers bit-perfect audio signal to your dac(provided your digital connection, from computer to dac, maintains the 'integrity' of the data).
Sounds allround better than iTunes to me, but notably, the bass is so much tighter and extended!
iTunes by comparison, isn't bit-perfect on pc. Though it is on mac, so maybe ideal there!
As i mentioned before, i truely believe in using iTunes/Foobar 'piggyback' on pc. I love iTunes straightfowardness, ease of editing album details, embedding album art, creating playlists of AAC files for iPod Touch, handling audiobooks, etc, etc, etc. So my music collection 'lives' inside of iTunes, a place that's GREAT for keeping my collection tidy!
Once your library's nicely organised, you then install Foobar and all it's plug-ins. Then it's just a matter of specifying in Foobar, the location of your music. Foobar will 'see' all of your collection, complete with album art, the works. Not been able to make it see iTunes playlists however, though it's easy to create some Foobar playlists.
And of course, you can fire up Foobar OR iTunes when you want to play your collection.
Regarding Airport Express, maybe someone knowledgeable on them can help you with that! I'm seriously considering the MTech Hi-face, with a quality digital co-axial lead, into my Dacmagic. My Wireworld Ultraviolet Usb cable is fantastic, but the MTech interface, with it's anti-jitter circuit, sounds even better!!