In Vegas, create a "5.1 Surround DVD" project.
Load the stereo wav you exported in Womble. This will be your reference file and will be muted out of the final mix.
Drag in each of your six mono files into individual tracks. Label them, so you know which is which. Check the alignment (I usually slam them all as far left as they will go) then GROUP them together so they will be edited and moved together. This is VERY important.
Set up the correct sound panning for each of these tracks so that they go to the correct channel in the final mix.
If your export had audio drift issues, here is where you would squeeze your stereo reference file the required number of frames. This method has been quite effective at "re-synching" a file for me. Squeeze the source, then align the "unsqueezed" files at each edit point.
Using your ears and eyes, align the audio to the reference file.
Add in new tracks with the deleted audio as necessary. Split the main movie according to the splits your ears tell you, line up a new scene, realign everything afterward. Keep going through this process until all your edits are re-created. Vegas has lots of fading options that can make for smoother transitions than straight cutting. Experiment.
SAVE OFTEN!!!
When you're satisfied, mute out the reference channel, then select "Render as" from the file menu. Be sure you're exporting to a 5.1 DVD.
Volunteer at a soup kitchen and use the downtime to help out somebody in your community. When you get back the file should be done.
Load the final video file with your new Audio file into a new (temporary) Womble project to preview how well they synch up. Pay special attention to the places you edited. If necessary, make changes and re-render the AC3 file or, even the Womble project if you notice issues in the video. It takes a lot of finessing.
I have created a surround file the way you described it with Vegas.
I then imported this soundfile into Womble and edited the video and cut the audio to fit the video.
I then exported the movie (m2v file), and checked if it still was surround sound. According to my computer, it was AC3 5.1 surround.
Then to double-check it, I let DVD Lab Pro split the audio from the m2v file, I split the 6 audiochannels again into 6 mono channels, but now suddenly every channel is the same. Each channel has suddenly the voice from the center track in it.
Do you know if I did something wrong or what is going on?