The official starwars.com announcement mentions Dolby 2.0 Surround sound, which is decoded into 4 channels as described by Moth3r, above. However, it does not specify AC3 encoding and AFAIK, does not rule out the possibility of a PCM soundtrack (although it's unlikely given the AC3 2.0 tracks on the '04 release). Perhaps Neil or Moth3r can set me straight here if I'm wrong.