Been asked about this.  

User wants to tie his iTunes into the LAN so he can play his MP3 collection though his 5.1 system.  Hes on a MacBook, so it appears most of the digital controllers wont work.  Anyone done this before?  We already know APple appear to do something that will work, but the relability of them raises some questions after reading a few reviews.

Airtunes or something Apple calls it?

Sorry cant help on the Mac front...I use my 360 for this job but its a Ã,£280 solution and you need XP and media player 11 or Zune.