Doesn't look like a Dolby Surround port, then again I never seen a Dolby port before. Ain't a Internet port either as it has Wifi.
I expect Pro Logic II, considering the Wii is going to be cheaper than it' rivals. The AV cable will carry video and Pro Logic sound, just like the Gamecube.
If it had Dolby Digital it would have a Optical or Coax digital port. Then again AV cable might have those ports but I highly doubt it.