Encoding AC-3 Audio 5.1 channel to dvd using DVDlab Pro

[dlots2000]

HI Hope you can me out this one has been driving me nuts

Here is the situation
I have a highdef tv broadcast that i have converted to standard dvd mpeg2. No problem there. I have demuxed the audio and video leaving me with an mpv and ac3 file. I have thouroughly checked the audio and video files out and they seem fine.
After trying many programs out. DVDLab seems to be the only one that supports 5.1 channel AC-3 sound correctly. However when i compile the dvd. it doesn't take the sound at all and gives me a dvd with mpeg2 audio. which has no sound.
Any help you could give me in this regard would be most appreciated

Thanks
Shaun

[awlchu]

What are the specs of the 5.1 stream?

What bit rate? Any bad sync frames? What tool did you use to confirm the AC3 ES is valid?