CS5, Windows 7.

Hi, here is what I've done:

Adobe Premiere: mix a 5.1 track, exported as .wav.
Soundbooth - verified my file has 6 channels. It does, and it plays fine.
WAV to AC3 Encoder: Encoded my .ac3 file.
Opened .ac3 file in VLC media player - plays fine, nothing 'missing'
Dropped the file into Encore. Played the file in the preview - rear channels not playing.
Exported to DVD disc. Rear channels not playing in DVD player, file is playing as a 2.0 file, except what should be coming out the rear, which isn't playing at all.
DVD Player audio info says 3/2+LFE.
VLC file info for the .ac3 is 6 channel.

What have I done/not done? if someone can help me, my film is showing the local art centre 6th Jan and my sound isn't working as it should!!

Desperate for clues!

Thanks,
Russ